bronto

This morning as I start the car to go to work I hear a whirring noise, not constant at idle, disappears mostly as revs increase.

All the external belts & hoses were replaced 14k miles ago. Timing belt at 58k, now 84k.

Ideas? I'm supposed to drive to LA this afternoon.

atb

Only whirring I've heard is from a torque tube. Is it for sure coming from the engine compartment?

FlyingDog

Since you have a 79 the square tooth timing belt makes a louder whirring noise than most belts, but that shouldn't be new. As Adam says, the only other thing should be the torque tube.

Bill Ball

Have you located the general area from which it emanates? Careful poking around with a length of heater hose or a vacuum cleaner hose held to your ear can be very helpful, while keeping in mind that bearing nosies can be conducted along structures. Try to find the loudest spot for the noise.

I've had a whirring bearing in the driveline for at least the last 3 years. It's very noticeable, sounds like a noisy fuel pump, but disappears once I put the transmission into gear. I can't pin down its source. I've just driven the car normally with no problem.

Whirring noises in the engine compartment can have lot of sources, most not very concerning. The air pump is a common source, from which I've had noise at one time that resolved on its own. Under that is the AC clutch. It has a large bearing that can go south. Not nice, but not critical to running the car. Power steering pump and the alternator would be sources on the other side. Anything seeming to come from under the timing belt covers would be of more immediate concern, although much less so in a 79 than in a 928 with a 32 valve motor.

bronto

I just went out to listen again, and it's gone - or at least very faint.

Let's hope it's nothing...

Bill Ball

Most likely. I've got some minor accessory belt/pulley squeaks on start-up right now that I'm ignoring, although I will get to them sometime soon. The 928 motor is usually pretty quiet, so little nuisance noises are very apparent. It's good to give them a decent evaluation to be more confident that its not important, like a water pump or tensioner bearing. I get real nervous if I can track the noise to those areas in my S4.

Fabio421

I had this problem once. It got progressively louder over the course of Rennsport Reuinion. It souned like a PS pump whine X 5. I had a few others at Rennsport Reunion listen to it and everyone thought it was the PS pump.

When I poked around I found that it was only the alternator pully rubbing against the belly pan. I had bottomed out coming out of a gas station parking lot while driving to Renn Reunion and since I was driving fast I didn't notice the sound until I got there. I just pulled on the belly pan a little and it went away. Hopefully this is your problem.

touay001

Hi Bill,

I had/have the same noise as you have described for 5 years now. It drove me crazy. I took the car to a few places to diagnose the noise, and I was told by a Mercedes trans specialist it was hydraulic noise within the hoses (or valve body) What made me consider his diagnosis is that the hoses where new. He said it does not warrant removing the trans.

Bill Ball

Interesting. So, not a bearing, but "hydraulic noise." I've been suspecting a worn torque converter bearing or primary pump that quiets down once put under a load. Whatever it is, it has been unchanged for years. I did have some problems with the valve body - I lost the downshift into first gear 4 years ago for a while. I "reasoned" it was probably a sticky 1-2 shift valve, since nothing else was wrong. I changed the fluid and added some trans cleaner and the problem went away immediately. It returned once a year or two later, but a repeat treatment fixed it and it has been fine for years since. I don't recall hearing the noise then. Anyway, as long as the noise is stable and there are no functional problems, I'm leaving it alone.

algie928s4

Suggest you buy one of those mechanics stethascopes, well worth the small $$$$

largecar379

might also be the air pump.....

had sort of the same noise on mine, rpm related/not speed related, removed the air pump and no noise.

--Russ

Bill Ball

Agreed, these are real good for "mechanical" noises, and everyone should have one. They are not useful for belt or pulley noises or air leak whistles, whereas a hose can be used to generally locate the loudest area for any kind of noise.

Landseer

Check to see if the fan blades might be beginning to touch the lower radiator shroud, which would indicate motor mounts sinking.

bronto

Well, I made it down to LA with no problem, but the noise has been there intermittently. I can best describe the noise is like one of those big supercharges they mount on big block chevys. Sounds really cool if it were supposed to be there Sound alters according to rpm, not speed.

Could this be fuel pump related? Is was pretty loud with the tank nearly empty; I stopped to fill up and and when I started it again it was much quieter. I know there's a pump in the tank; is there also one up front? It could be a coincidence though. It also occurred to me (after it quieted down and I couldn't test it) that it might stop/go according to if the heater blower is going or not.

Car is still performing as well as always...

Bill Ball

Fuel pumps are in the back. The fuel pump wouldn't change pitch with RPM. You've got lost of things to check for round the motor.