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      12-14-2015, 10:26 AM   #1
Knoxes
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Rpm related noise

I have a 07 e86 with ~70K miles. I've had it for about a year and I notice this "whir" with the engine rpms sometimes - almost like a viscous fan. It's especially noticeable after I've been on the freeway for some time, and pull off. At the first rev after that, it's pretty predictable. It's not bothersome, but it does take away from the normal 3.0 engine grunt. I've searched a bit, but I haven't found any other threads (might be due to my search terms). Any ideas what this is?
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      12-14-2015, 10:35 AM   #2
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I have this as well. It is the heater fan for me. If I turn the fan off the noise goes away, if I turn the fan to full blast for 5 seconds and then back to auto it goes away. If the fan is set to auto when I start the car it will "whirl" with motor RPM.
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      12-14-2015, 01:14 PM   #3
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I would be surprised if it's the HVAC fan, but I suppose that it's possible. This sounds is very much tied to the rpms.
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      12-14-2015, 01:51 PM   #4
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Yes I agree. I was surprised. If I rev the engine the whirl from the HVAC would increase in direct correlation to it. If I turn the HVAC fan off it went away. Give it a try and see if that is what it is. The only explanation I can think of is the fluctuation in the voltage on the system on engine RPM. I see 12V at idle and up to 14.4V with the increase in RPM. I took my dash apart to get at the fan and it is a pain. I decided to live with this until the fan dies.
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      12-15-2015, 11:05 AM   #5
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I'm currently chasing something I thought was drive train noise on my wife's 328xi (also the N52). But....it goes away when I turn off the AC, which was a surprise-- so it at least appears the clutch on the compressor is effective.

Go ahead and try turning the AC switch on and off and see if it makes a difference.
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      12-15-2015, 01:24 PM   #6
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That makes more sense to me. I can't say that it was more noticeable during the summer though. But I run the a/c almost year round to deal with the humidity.
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      12-15-2015, 07:01 PM   #7
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Quote:
Originally Posted by Knoxes View Post
That makes more sense to me. I can't say that it was more noticeable during the summer though. But I run the a/c almost year round to deal with the humidity.
It could also be a worn alternator bearing.

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      12-16-2015, 10:52 AM   #8
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Quote:
Originally Posted by Karacticus View Post
I'm currently chasing something I thought was drive train noise on my wife's 328xi (also the N52). But....it goes away when I turn off the AC, which was a surprise-- so it at least appears the clutch on the compressor is effective.

Go ahead and try turning the AC switch on and off and see if it makes a difference.
I tried this last night. As soon as I turned the A/C off the noise went away. I tried it a few times. I still don't get why the noise would go away if I turned the HVAC fan to max and then back auto.
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      12-16-2015, 12:32 PM   #9
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Quote:
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I tried this last night. As soon as I turned the A/C off the noise went away. I tried it a few times. I still don't get why the noise would go away if I turned the HVAC fan to max and then back auto.
I've got a service appointment on the 31st. If you don't find out what it is before then, I'll let you know.

It could be that cycling the fan from max to auto cycles the compressor, but really don't have any idea at this point. Too many computers. Does yours have the automagic climate control (set to temperature)? That's what I'm working with.
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      12-16-2015, 12:39 PM   #10
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Yes I have the automatic climate control. Let me know what they find out. It would be nice to get this fix and not deal with the sound anymore. It drives me a little crazy but no one else notices it.
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      12-31-2015, 06:32 PM   #11
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Car was serviced today.

When I took the car in today, it wasn't making the noise as it was before, but then it's the A/C, and it's now 20F outside.

The tech did say that in the past, they've found similarly (written up, anyway) noises to be due to a low refrigerant level. They did find the system fill down to 8 oz, when the spec is 21 oz.

System was evac'd and refilled. We'll have to see if that addresses the issue or not.
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      02-11-2016, 10:01 AM   #12
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Mine is worse now that it's much colder outside. It's not the HVAC fan or the a/c compressor.
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      03-09-2016, 01:19 PM   #13
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I heard the fan spinning down after turning the motor off today. Since I had the A/C on, I'm assuming that was the aux fan.

It wasn't the same sound that I've been hearing. I'm beginning to wonder if it's the water pump bearings because I'm filling the reservoir with about 1-2 cups of coolant every 3-4 months. Maybe it's slow leaking?
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      03-09-2016, 02:52 PM   #14
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Pull the serpentine belt and see if the noise goes away. Turn each component by hand and check for resistance. get a stethoscope and listen to each item running off the belt.
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      03-09-2016, 06:28 PM   #15
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^WHS. Could be an idler or belt tensioner pulley.
These are a common wear item, and chatter when they get floppy.
Check the AC tensioner, too, although I think it's less common for those to go floppy than the main belt tensioner.
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      03-10-2016, 08:27 AM   #16
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Quote:
Originally Posted by longress View Post
Pull the serpentine belt and see if the noise goes away. Turn each component by hand and check for resistance. get a stethoscope and listen to each item running off the belt.
Won't that throw a bunch of codes?
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      03-10-2016, 11:28 AM   #17
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Quote:
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Won't that throw a bunch of codes?
No there's nothing driven by the Serpentine belt that can trip codes (the battery light might come on). This is just a pull the belt, start the engine and see if the noise is gone and then check everything that is driven off the belt by hand.

You obviously don't want to run the engine long because the water pump and alternator won't be turning but it's not a concern if only done for a couple minutes
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      03-11-2016, 08:03 AM   #18
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I thought there would be other sensors tripped by the lack of a belt. I don't have a shop manual - which tensioner is easier to access?
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      03-11-2016, 09:37 AM   #19
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There's only one for each belt. The main belt has a plastic cover that needs removed covering the torx or hex (can't remember). Swing the tensioner down to create slack to pull the belt. Pull the belt over the alternator pulley to remove and when reinstalling the last pulley the belt is slid over is that same pulley. Make sure you draw a diagram of how the belt is routed.
I know what you're saying now. The other pulley is an idler pulley. The tensioner (lower pulley of the two)you can see has the ability to move the idler does not. Sorry if that sounds dumb ��

Last edited by longress; 03-11-2016 at 09:53 AM..
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      03-11-2016, 09:52 AM   #20
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Here's a photo. If you google Z4M Drive belt and look at images it's all there.
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      03-11-2016, 01:05 PM   #21
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Yup, got it. Thanks, longress.

I freakin hate getting underneath this car.
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      03-11-2016, 01:20 PM   #22
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I drive mine up on low ramps... That gives me enough room to do a oil change. It also gives you peace of mind.... Nothing is going to collapse.

But agree with you about not liking going under the car.
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