# Whistling noise at part throttle- highway speeds.



## bmw325 (Dec 19, 2001)

I"ve actually posted about this before- and have taken the car to the dealer who didn't hear anything.

Basically, if I'm going at highway speeds (60+), and crusing w/ just slight throttle (like you'd do to maintain a certain speed), my car makes a kind of whistling noise. I don't think its belt related because it doesn't make the noise when revved at idle. I'd guess it has something to do w/ the air intake or throttle body. I've also noticed that the problem is more likely to occur in warmer weather.

My car is an 01 325i w/ a manual transmssion. Has anyone else noticed this? I'd just like to get some possible ideas of what could be wrong to get my dealer pointed in the right direction. I'm hoping its something real simple like changing or re-seating air filter- but have a feeling its something w/ the throttle body.

TD- I know that you may find this post a bit .org-ish-- but I have actually gone to the dealer, contacted BMW via phone and email, and searched the web. 

Any ideas? I'd appreciate it if you guys would listen closely the next time your cruising the on the highway w/ part throttle.
Thanks.


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## webguy330i (Jan 9, 2002)

Hey rob, could it be your tires? I remember a few people complaining about the whine from the rear differential also. Basically I'm wondering if it's definitely coming from the engine bay or not. It could be wind noise too, does it do it at WOT at the same speeds?

It could be that the throttle position alters some sort of valve in the intake system (not the TB valve; more like a secondary intake runner or something) but I'm not sure since I haven't dissected the intake yet. I think it's different for the 325 anyhow. Sorry I can't help ya out.


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## bmw325 (Dec 19, 2001)

Hey Chris--
thanks for the ideas.
Its not wind noise or tire noise because its very throttle dependent-- if I give more throttle the noise instantly goes away- and likewise if I completely remove my foot from the the throttle. I was thinking about the differential too-- but i'd think that a differential related whine would be dependent on speed- throttle position wouldn't really matter. Its kind of hard to place the noise-- it just kind of "makes is self known" I'm pretty sure its coming from the front of the car though. Unfortunately, I can't recreate it at idle-- which is of course how the dealer tires to trouble-shoot it. THe only thing I can think of is to get a dyno w/ a big fan in front and listen to various portions of the engine bay while its running. I've also toyed with the idea of hooking up some sort of tape-recorder w/ microphone and placing it on top of various poins of the intake-- but am afraid of dire consequence if the microphone were to become unstuck.

SO I take it your 330 never makes any kinds of intake or differetial whining or whistling noises? Actually, I think the intake systems between the 325 and 330 are similar but the 330 has an even larger intake box.


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## johnlew (Dec 25, 2001)

Differential noises are definitely speed and throttle related. It would be more accurately described as a whine. If the noise goes away when letting off the gas or giving more throttle this could be it. But it should sound like it's coming from the rear.


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## bmw325 (Dec 19, 2001)

John-- yeah I agree that if it was diff-related it would be noticelable from the rear. Although I can't exactly pinpoin the sound-- its definitly not coming from the rear.


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## webguy330i (Jan 9, 2002)

rob, why not have the tech at the dealership go for a ride with you? I've had them do that a couple times for rattles and what-not, they never seem to make a fuss.


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## bmw325 (Dec 19, 2001)

Yeah- I've had them ride w/ me and they claim that they can't hear it- i've actually had 2 different techs ride w/ me. I know i'm not making it up- my girlfriend notices it too sometimes. I just need to book an appointment w/ a different dealer I guess...


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## The HACK (Dec 19, 2001)

robg said:



> *I"ve actually posted about this before- and have taken the car to the dealer who didn't hear anything.
> 
> Basically, if I'm going at highway speeds (60+), and crusing w/ just slight throttle (like you'd do to maintain a certain speed), my car makes a kind of whistling noise. I don't think its belt related because it doesn't make the noise when revved at idle. I'd guess it has something to do w/ the air intake or throttle body. I've also noticed that the problem is more likely to occur in warmer weather.
> 
> ...


Welcome to what us CAI owners called the "metallic hissing sound". All CAIs, since they remove the sound dampening air box, makes this sound particularly pronounced. At highway speeds the engine isn't lugging as hard and it's more likely that your throttle is more consistent, hence you notice what we called a hiss as a ligth whistle.


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## webguy330i (Jan 9, 2002)

*Re: Re: Whistling noise at part throttle- highway speeds.*



The HACK said:


> *
> 
> Welcome to what us CAI owners called the "metallic hissing sound". All CAIs, since they remove the sound dampening air box, makes this sound particularly pronounced. At highway speeds the engine isn't lugging as hard and it's more likely that your throttle is more consistent, hence you notice what we called a hiss as a ligth whistle. *


rob do you have an intake? If so that is most definitely the cause of the sound. If not, I'd still say it has something to do with the intake or fuel system.


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## bmw325 (Dec 19, 2001)

Dan, Chris-

I don't have a CAI. But what you said makes me think it could be a problem w/ my OEM air filter. That's my wishful thinking since that would be very easy to fix. Dan-- does this whistling with your CAI occur only under light throttle and at highway speeds?


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## Nick325xiT 5spd (Dec 24, 2001)

I've noticed the noise myself.
It's something I just ignore, it doesn't REALLY bother me, though I have tinnitus, so I'm trained not to pay attention to high pitched whining. :dunno: :dunno: :dunno: 
Nick


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