What is this ungodly noise?

[mattjd43]

Hi folks,

Hoping someone can help me diagnose this horrible noise. To me it sounds like an old dot-matrix printer from the 80s printing at a frantic speed. It presents on startup then dissipates, only to reappear above 1,000 RPM. The noise doesn't change with acceleration and is present in gear and in neutral. Any guidance would be greatly appreciated.

Details:

2011 BMW 328i xDrive
81,000 miles
Purchased in August 2016 with 70,000 miles
Oil changes done every 5,000 miles
Use only 93 octane unleaded, mostly Top Tier
Ran Carly BMW diagnostic, which showed no codes
Car is otherwise driving just fine

[MIKYZZ4]

Remove the belt, then start her up,
Did the noise disappear?
If so, you have isolated the problem to belts and pulleys.

[bmwdirtracer]

I agree that this is necessary....unless the belt is already part of the way off the tensioner pulley, when the engine is off. If the belt is part of the way off that pulley, engine off, AND it's making that terrible noise, DO NOT EVEN START THE CAR AGAIN, until after the tensioner assembly and belt have been replaced.

If the belt comes off that pulley, engine running, it will cut into the crankshaft seal, undo the engine's timing, and end up with parts of the belt inside the oilpan, and perhaps bend all the valves. Seriously, if the belt extends beyond the edge of the pulley, don't even start the motor.

If not, release the tension on the belt at the tesioner, remove the belt, and see if the noise goes away when you start the engine. If the noise is gone, spin each pulley by hand, and try to wiggle it on its axis. If it makes noise spinning, or wiggles, replace that pulley or item. Tensioner pulley is most likely, idler puller is also a failure item.

You might want to just go ahead and replace both, AND the belt, of course, while you're there.

[MIKYZZ4]

Thanks for the lesson Chris,
that's something I missed and hadn't thought of,
Thanks again for sharing your knowledge Chris, you're the best!

[dworthy]

+2

The belt change is recommended by BMW every 4yrs/50k miles. I have a rule of thumb: Second belt change replace all idle and tensioner pulleys. Has there been times where I could have just replaced only 1 pulley, sure but I don't want somebody coming back later for a second or third time for the same thing.

[bmwdirtracer]

Thanks for the lesson Chris,
that's something I missed and hadn't thought of,
Thanks again for sharing your knowledge Chris, you're the best!

You pointed to the most likely culprit, Miky....it's just that this particular engine (N51 / N52) likes to commit suicide-by-tensioner, so a quick check for whether the belt's falling off is wise. In fact, every time I open the hood on a car with this engine, I take a peek at that pulley.

[mattjd43]

*SOLVED!*

Thanks guys for all your input, especially you, Chris (and Miky!). I tried what you said, but when I started the car up sans belt, the noise was still there! What gives?

With the tensioner and pulleys eliminated as a source, I could better locate where the sound was coming from. It became apparent that it was coming from the oil filter cap. Putting my hand on the cap changed the pitch of the sound, and I could feel a weird vibration.

Knowing that the noise came from the oil filter allowed for a more accurate Google search, which revealed the following thread: http://www.e90post.com/forums/showthread.php?t=835145

Bingo! Had to be an oil filter problem and it sure was. Normally, I do my own oil changes. But being without a heated garage here in Central New York in winter means I'll have someone do it for me. I went to a local shop I'd only had my wife's Prius in to. They have a good reputation, are reasonably priced and convenient. Plus, I've seen a few bimmers in their lot for service. So I had them do this oil change a few hundred miles ago. Well, it appears they completely screwed up the install of the filter. When I unscrewed the oil filter cap, oil gushed out and the cap came off without the filter. Not only was the core that goes into the filter NOT attached to the cap, but it was wedged tightly into the filter itself; so tightly I ended up having to cut the filter off the core. The end with the small gasket was solidly inside the hole leading to the engine. That sound must have been caused by obstructed oil flow into and out of the filter. Sure enough, I properly installed a new filter and started up. Sound is gone. Engine sounds as good as the day I got it. Thankfully, the filter itself (Mann) was a bit crushed in parts but otherwise intact. I just hope no real damage was done to my engine. Any thoughts on the effects of running a car for a few hundred miles with a messed up filter?

Really appreciate the info you guys gave. It led to the identification of the problem and a solution. Hope this thread will help someone else in the same situation.

Thanks again.

--Matt

[shadowpuck]

wow....

BMW actually has a TSB on a very similar issue with the N52 if someone forgets to install the inner cage....

[bmwdirtracer]

Matt,
Thank You!
You have just proven my life long belief that an "instructor" can always learn as much as his "student", in any given situation. Shadowpuck, who is also a BMWCCA instructor, will agree, I'm sure.

Certainly, I always change both o-rings, and click the filter into the cap. Certainly, I have noticed deformed filters....(although I've never heard them make noises). Still, YOU have fixed your noise issue, through scientific research and observation....and you've just provided the members of this forum a crucial possible explanation for other people's 'screaming" noises on an N52.

I will look for this possibility, in the future, and I'll try to remember the lesson you shared here today.

Chris

[shadowpuck]

absolutely!! seems like any time i teach a subject (either in my profession or my hobby) to someone else i learn something new along the way.

[328 Power 04]

In just 2 posts ever, you post the problem, and find your own solution. That's awesome. Hats off to you.