Whinning noise from tranny/diff on auto? Please say it isn't so.

[tcmarley]

I had a problem with some clicking noise coming from the rear of my car when pulling away from a stop or backing up from a stop... I thought it was the RSM's going out so I replaced those and the noise didn't go away. After reading up on this forum I realized it could be the diff bolts coming loose and it was recommended to tighten each one a quarter turn. I had my shop do that (and it resolved the clicking problem) and now I am getting a whinning noise upon acceleration and when I coast to a stop.

The noise is coming from the auto tranny and is not related to the engine speed. It does increase as I accelerate until the auto shifts down and then starts again through the next auto gear. Also when I come to a stop the tranny is still turning and as it slows the noise tails off.

Did they tighten something too tight that the flex plate or something else is now rubbing? Is this the sign of the auto's or diff's demise and the start of my 5-speed conversion? I was told not to change the transmission fluid because it would bring on transmission failure... is this noise because of the tranny or differential fluid being low or it needs to be changed? There is 98K on the car now. From the receipts that I have the last time the diff fluid was changed was at 55K.

The original owner had the rear diff swapped out for a higher ratio and the second owner had the original put back in... Would that entail draining the tranny fluid each time? I was told if you have never changed your auto tranny fluid, you should not change it or you should expect bad things to happen in your transmission. If the tranny fluid was changed sometime in the past (when the diff's were swapped out) then I am going to have them flush it and replace it with something good (RedLine D4-ATF) to hopefully get a few more miles out of the auto. I will have the diff fluid replaced also with Redline and hopefully smooth everything out and quiet everything down?

[deilenberger]

I had a problem with some clicking noise coming from the rear of my car when pulling away from a stop or backing up from a stop... I thought it was the RSM's going out so I replaced those and the noise didn't go away. After reading up on this forum I realized it could be the diff bolts coming loose and it was recommended to tighten each one a quarter turn. I had my shop do that (and it resolved the clicking problem) and now I am getting a whinning noise upon acceleration and when I coast to a stop.

Which "diff bolts"?? Need a more accurate description.

The noise is coming from the auto tranny and is not related to the engine speed. It does increase as I accelerate until the auto shifts down and then starts again through the next auto gear. Also when I come to a stop the tranny is still turning and as it slows the noise tails off.

You are contradicting yourself in the paragraph above. You say (and I'll sort them out so you can see the contradiction):

1. Noise is not related to engine speed

2. Noise increases in EACH GEAR as you accelerate, and falls back when the transmission upshifts.

Think on this a moment - what happens when the transmission upshifts? Engine RPM's drop (watch your tach) - sounds like it IS engine speed related unless you meant something completely different.

Did they tighten something too tight that the flex plate or something else is now rubbing? Is this the sign of the auto's or diff's demise and the start of my 5-speed conversion? I was told not to change the transmission fluid because it would bring on transmission failure... is this noise because of the tranny or differential fluid being low or it needs to be changed? There is 98K on the car now. From the receipts that I have the last time the diff fluid was changed was at 55K.

Too many questions - not related - in one paragragh makes it hard to reply.

1. Did they tighten something too tight? Maybe. Depends on what they actually tightened.

2. Is this the sign of the auto or diff's demise? Unlikely IMHO since it started when your shop did some work under the car.

3. Is the noise due to low fluid? Unlikely IMHO since it started when your shop did some work under the car. Unless they drained fluid out - there is no reason to correlate the two.

The original owner had the rear diff swapped out for a higher ratio and the second owner had the original put back in... Would that entail draining the tranny fluid each time?

Again - please try to keep your thoughts in logical paragraphs.. you're pretty much jumping from one thing to another. Sorta like a Vulcan mind dump on screen.

The transmission and differential are not even near each other - and there is no requirement to change both fluids if one fluid is changed, although it might be a good service procedure to do so. One is under your shifter - the other is under the trunk. Only a driveshaft connects them.

I was told if you have never changed your auto tranny fluid, you should not change it or you should expect bad things to happen in your transmission. If the tranny fluid was changed sometime in the past (when the diff's were swapped out) then I am going to have them flush it and replace it with something good (RedLine D4-ATF) to hopefully get a few more miles out of the auto. I will have the diff fluid replaced also with Redline and hopefully smooth everything out and quiet everything down?

Well - you're taking the shotgun approach (throw stuff at it until the problem goes away..)

Lets think this through together:

1. You had a clicking noise. You haven't really described if it was speed, engine or road-surface related. It would help a whole bunch if we knew that.

2. Your shop (are they a BMW shop? A local gas station? Some guy in a garage behind his house?) tightened some bolts and now you hear a new noise - a whine that seems to increase as road speed increases in each gear, and then fall back when the transmission upshifts.

OK - some diagnostics questions:

1. Have you tried turning your radio off? Alternator whine sounds just like what you're describing.

2. If it's not radio related - describe to the best of your ability where the whine is coming from. This might require you having someone else drive the car while you move around in it trying to localize it.

3. What bolts? Really need to know what your shop tightened.

4. Think about the correlation between engine speed and road speed in each gear - and decide is it engine speed related?

5. While moving - perhaps at 30MPH or so - in a safe environment - try shifting into neutral for a moment (do NOT go to PARK or any other gear) - and coast - see if the noise goes away, decreases, gets louder. Let us know.

I'd recommend against changing the fluids at this point since you really have no idea what the real problem is. RedLine supposedly makes a fluid compatible with the horrendously expensive fluid BMW used in the lifetime fill automatic transmissions - but I've heard rather mixed reviews of it. Usual auto-trans failures are usually slipping in gear or very slow or harsh shifting. Whine is not a common failure mode. And new fluid is unlikely to cure whine if something like a bearing has gone bad.

Get back to us with some details and mebbe we can help you out.

[tcmarley]

Thanks for the line-by-line critique of my post and giving me a lesson on proper posting etiquette???

After searching more on this forum about the noise that I am hearing I think it is definitely coming from the differential, but here are the details:

1. Noise is not related to engine speed

2. Noise increases in EACH GEAR as you accelerate, and falls back when the transmission upshifts.

Think on this a moment - what happens when the transmission upshifts? Engine RPM's drop (watch your tach) - sounds like it IS engine speed related unless you meant something completely different.

I will try to explain this better....

1. The noise I hear is a hum coming from the rear of the car and sounds like from the differential or drivetrain. As the RPM's increase and the car accelerates the hum gets louder until the transmission upshifts and then it starts to build again. It is a metal on metal humming noise that sounds like gears meshing together or metal slightly hitting some other metal object that creates a whirring noise that sounds faster as the car accelerates. This noise is coming from something that is spinning inside of the transmission or differential and I can be coasting almost to a stop and it is still winding down although the engine RPM's have already dropped to idle levels (i.e. coasting to a stop at a stop light).

1. Did they tighten something too tight? Maybe. Depends on what they actually tightened.

2. Is this the sign of the auto or diff's demise? Unlikely IMHO since it started when your shop did some work under the car.

3. Is the noise due to low fluid? Unlikely IMHO since it started when your shop did some work under the car. Unless they drained fluid out - there is no reason to correlate the two.

I originally was trying to find the source of a clicking noise that was coming from the rear of my car and I came across a post on this forum that was exactly the symptoms and noise I was getting. It was a clicking noise that was heard when shifting from Park to Reverse or Park to Drive when the car was completely stopped. The post said this could be attributed to loose differential bolts where they mount to the subframe and that tightening these diff bolts 1/4 turn would resolve the issue. I had my shop check the bolts and they said that they were loose and did exactly that.... tightened them 1/4 turn. This resolved the clicking issue.

You did give me a few things to check.

OK - some diagnostics questions:

1. Have you tried turning your radio off? Alternator whine sounds just like what you're describing.

2. If it's not radio related - describe to the best of your ability where the whine is coming from. This might require you having someone else drive the car while you move around in it trying to localize it.

This is not related to anything but the transmission or differential.... The noise is coming from the rear of the car and not the engine or radio. It is not heard when the car is in park but only when accelerating/decelerating in any gear. It is very noticable from inside and outside the car in first and second but can't really be heard in third, forth or fifth. BTW, I have replaced everything but factory head unit in the crappy HK system and there is no alternator noise present.

3. What bolts? Really need to know what your shop tightened.

I had my local BMW-Only repair shop which I have confidence in their mechanical abilities, tighten the 3 carrier bolts that mount the differential to the subframe

5. While moving - perhaps at 30MPH or so - in a safe environment - try shifting into neutral for a moment (do NOT go to PARK or any other gear) - and coast - see if the noise goes away, decreases, gets louder. Let us know.

Yes... I should try this. This will help determine where exactly the noise is coming from.

As I posted the differential has been swapped out twice and when the original ratio was put back (after 2+ years with a higher diff) I don't know the condition it was in or how many miles were on the differential that was put back in. That was about 40,000 miles ago. I will have my shop check the fluid levels and rule that out. I am happy with their service and will let them diagnose the problem since it wasn't there before they worked on it last.

Also, I usually do most of my own work on the routine maintenance and DIY projects, but when it involves internal engine, transmission, or differential problems I leave it to someone who has much more experience than I do. Thanks for your reply.