Whining varies with RPM, more noticeable when AC is on

[shaytanabyad]

Title says it. My car whines when under load. At lower speeds it's more noticeable as the whine increases in pitch with the RPMs so the engine eventually drowns it out to a near unnoticeable pitch. It's worse with the AC on. The whine doesn't change with changes in the blower speed so I don't think it's the motor. Could my compressor be semi-seized? It's not road noise and it doesn't happen when in neutral.

I've done a lot of work on my e34 but not too much on the e90. Thoughts would be appreciated.

Thank you.

[Pyewacket69]

Title says it. My car whines when under load. At lower speeds it's more noticeable as the whine increases in pitch with the RPMs so the engine eventually drowns it out to a near unnoticeable pitch. It's worse with the AC on. The whine doesn't change with changes in the blower speed so I don't think it's the motor. Could my compressor be semi-seized? It's not road noise and it doesn't happen when in neutral.

I've done a lot of work on my e34 but not too much on the e90. Thoughts would be appreciated.

Thank you.

Typically what you are describing is drive-train noise, and its quite common for the rear differential to whine under load. The A/C really doesn't care if the car is in gear, neutral, under a load or not, and the compressor is controlled by a clutch that free-wheels when the A/C is off, so I'm guessing the open ductwork under the dash is enhancing the sound level inside the passenger compartment.

I'd put my money on a bad bearing somewhere, or a mis-aligned differential gearing.

[shaytanabyad]

Thank you for the feedback. How would I go about investigating this on my own? Bad bearing where? Mis-aligned diff gearing sounds scary. Ha. Any way to take it off the potential issue list?

[Pyewacket69]

Thank you for the feedback. How would I go about investigating this on my own? Bad bearing where? Mis-aligned diff gearing sounds scary. Ha. Any way to take it off the potential issue list?

Unfortunately, its often difficult for the amateur to discern exactly from where a bearing noise is originating. My suggestion is to take the car in to a reputable shop that you trust and have someone ride with you to hear the noise, and then isolate it.

If its the differential, it could be a big problem, but more likely its not anything you need to worry about. Slightly misaligned gearing there can create discernible whining noises but still not cause any problems for tens of thousands of miles. And, its rare that it just occurs out of the blue, but more like a gradual, long-term process. If you don't track your car or drive "race-car" style, odds are you have nothing to worry about in that area.

[mechanicii]

Sorry for the late reply.

Just wondering is your whine RPM related, or speed related, does the car whine when you race the engine in park?
If its RPM related I would say it is related to the alternator whining and not drive train, reason I say this because you say in your post its noisy at low speeds.
Simple test is to remove your fan belt which in turn would eliminate the alt. turning.
I hope this helps.

[Pyewacket69]

Sorry for the late reply.

Just wondering is your whine RPM related, or speed related, does the car whine when you race the engine in park?
If its RPM related I would say it is related to the alternator whining and not drive train, reason I say this because you say in your post its noisy at low speeds.
Simple test is to remove your fan belt which in turn would eliminate the alt. turning.
I hope this helps.

The OP stated the whine is present under load, so I'd bet against the alternator. Still, you offer a quick and relatively painless way to find out for sure.

[Pedro Rabie]

if you're over 60K miles alternator is my bet...

[meQD]

Typically what you are describing is drive-train noise, and its quite common for the rear differential to whine under load. The A/C really doesn't care if the car is in gear, neutral, under a load or not, and the compressor is controlled by a clutch that free-wheels when the A/C is off, so I'm guessing the open ductwork under the dash is enhancing the sound level inside the passenger compartment. I'd put my money on a bad bearing somewhere, or a mis-aligned differential gearing.
I got same problem. It set out whining right from starting the E90 and keep whinging all the time even when its in Park.
Its more noticeable at 1.5RPM and by ascending rpm it goes to fade or less noticeable at least.
Some dealer removed the belt from the AC compressor and after that the noise was gone.
They told me the problem is the compressor bearing but you have to change the whole compressor because they're not separate parts.
That would cost me too much $$ :(
Please help..

[928]

I've been having the same symptoms. Took it to the dealer yesterday and the A/C was low on refrigerant due to a leaking schrader valve on the low side. When I was showing the SA the whining noise, when we would turn the fan button completely off to disable the climate control the wine would disappear. They think the whine is coming from the blower motor but the whine gets worse with engine RPM as described above, so I think it is the compressor. It also is less noticeable now that the system is full of refrigerant. OP, try turning the fan button down to the completely off position and see if the whine disappears, that will isolate it to climate control vs. something else.

[NY Scotsman]

I had a similar issue and found that the accessory belt tensioner spindle was a little bent and out of alignment.

Replaced belt tensioner and belt and it has been whine free since.

Let us know when you have a solution.