Help Needed for Whistling M5

Hi there. I am the (normally) very happy owner of a 1991 Alpine White E34 M5. This is my first post on this Board. I need some help eliminating a very annoying noise. It is a whistling noise. Starts when the car is just starting to warm up. The engine has probably only been running five minutes or less. The whistle is not present when the car is idling. It comes on at about 1400 rpm and continues up to about 2200 rpm when it is lost in the general engine noise. It gets higher in pitch as the rpms increase. It is louder when the engine is hot.

First thought was a vacuum hose. All have been checked and seem fine. Any suspect one was replaced. Next thought was the alternator or something being run by one of the belts up front. All belts were removed and the engine run (briefly). The noise was still there. Starter fluid has been sprayed on the connectors from the throttle bodies to the intake manifold (looking for a funny idle problem) but there was no sign of any leak there.

Then my mechanic (Bavarian Professionals in Berkeley) traced the noise with a sophisticated stethoscope which allows you to home in on one frequency. The noise seemed o be coming from behind the harmonic balancer. They removed the front crank seal. There was a groove being worn in the crank seal cover so that was ground out, everything was lubed up, a new gasket installed and put back together. The noise was still there.

Next I replaced the cam chain tensioner with the newer version from the E36 M3. No change in the noise. Recently we have dropped the oil pan and replaced the oil pump. They inspected the oil pump drive chain and sprockets and there was no sign of unusual wear or anything. No change in the noise.

The cheap solution would of course be to buy earplugs, but then I wouldn't be able to hear that wonderful roar of the engine. Has anyone had a similar problem? Were you able to fix it? How? Anyone have any suggestions?

Sound travels through steel and internal sounds are all throughout the engine. Hearing it is easy, what is making the noise is difficult.
Well you know that now.
If you are sure it is not an intake gasket or other vaccum leak!

First make sure it is not the throw-out or pilot bearing.
Depress and release the clutch pedal to detect throw-out bearing noise and put transmission in gear with clutch depressed to detect pilot bearing noise. I know of one case where a bad pilot bearing made the throw-out bearing squeel on the clutch pressure plate spring fingers.

Warm up the engine and then remove the V belts.
You can run the engine for several minutes without the v belts to diagnose the noise. V belt on warn pulley, alternator and waterpump bearings can make lots of noise. Water pump is a 60-65K mile item.

Thanks, Rod, I neglected to mention that clutch in or out makes no difference to the noise, nor does the gear it is in. I did mention in the post, but perhaps not clearly enough, that all the V belts were removed when the engine was hot and the whistling continued.

My gut feeling (hearing?) is that it has to be a vacuum type leak. I am going to start disassembling on the intake side and see what gives.

Anybody have any other suggestions? TIA.

Alan,

I have a whistling noise as well. It is not too loud, but is definitely there at the same RPMs you describe. I wouldn't say that it is something that needs earplugs, just a noticable background noise.

The only information that I can pass on is that I first noticed it after replacing my Resonance Flap controller. Since you are going down the vacuum path and the RF system is vacuum controlled, this may give you a place to look. You may want to try to disconnect the RF controller and see if the whistling goes away. I will see if I can find the time to experiment as well.

Good luck, let me know if you find anything.

Kris

my newly acquired M5 has exactly the same whistle, under exactly the same conditions.

I hope to begin isolating the noise this weekend.

Brad
1979 635CSi
1981 745i
1991 M5
1992 735i

Crankcase is plumbed directly to the intake air box that is it.

I have not had a spare moment to fault isolate a similar whistle on my M5, and was wondering if you had enjoyed recent success with your efforts.

Brad
1979 635CSi
1981 745i
1991 M5
1992 735i

hi all,

i just bought a 1991 M5 and it is truly an awsome car!!!

i have the same Whistling Sound problem. i notice every time i step on the gas, the noise will increase.

it is not a big problem 'cus once the rpm is high enough, the engine sound covers the Whistle.

but i would like to fix that. does anyone solve the problem?

thanks

I am wondering if anyone resolved the whistle mystery? I have the same problem with my 1991 M5. It seems to appear once the engine warms up.

Hello All,

I know this is an old post, but I finally figured out what the problem is on my 1991 M5. Though I have had this problem for a long time, it didn't really bother until this last week. The whining noise got even loader where I can't even hear the engine, so it was time to figure out where it was coming from.

The cause was the clutch fan. The first thing my mech did was remove the entire fan assembly (fan and clutch). Started up the car and the whining noise disappeared. Running without a fan for a few seconds will not hurt the engine. Replaced the clutch fan with a new one and the whining noise is gone.

thanks !

when I saw this post just now, I was focused on the initial post and after reading it, went back to see who else had contributed.

THAT'S when I realized - this is the thread I responded to shortly after bringing my M5 home.

I must say, it's a durable fan clutch, because mone still operates just fine, but that annoying whistle has never gone away. I'll be ordering a replacement fan clutch tonite!

I have been bugged since I've owned the car, but not to the point for exhaustive investigation.

Thanks for following up Alan.

Brad

it now sounds like that was the obvious thing to do....
congratulations !!!

wonder if it was just a nicked fan blade or the fan clutch...

see you in the hills :)

Before you purchase a new clutch fan, remove the one from your car and start it up and see if the noise is gone. This is a simple test. I don't know if my issue is the same as yours.