Whiring sound from the rear end?

[markmalin]

Hi guys,

I've had my 85 Carrera nearly 4 weeks now and love it. Last weekend I swapped out the previous owner's exhaust setup (headers and M&K) and put back in the OEM system. Much quieter...but I notice something I was probably never hearing before due to the sound of the PO's exhaust. When I slow down there is a whirring sound (high pitched - almost like a faint fire-engine siren) that decreases in frequency as I slow down, then stops about 20 mph. If I put the clutch in, am in neutral, or in gear, still hear the same sound. The change in frequency doesn't follow engine RPM, but follows the speed of the car, so as the car slows down the "siren" frequency gets lower as the speed decreases, until 20 MPH and then it stops. (It's high pitched...about like a fire-engine I guess)

Last night I jacked up the back of the car to rotate the rear wheels - didn't hear anything out of the ordinary. Any thoughts? I figured tonight I'd check the trans fluid. I know the PO put Swepco in the transmission (and I have some left if I need to top it off).

Thanks
Mark

[wildcat077]

Mark,

You will discover all sorts of "Porsche exclusive" sounds with your car ...
I've had mine for three years now and i'm still trying to figure out if the whirring sound is from the gearbox,the engine or the rear wheel bearings !

Cheers!
Phil

[markmalin]

Originally Posted by wildcat077

Mark,

You will discover all sorts of "Porsche exclusive" sounds with your car ...
I've had mine for three years now and i'm still trying to figure out if the whirring sound is from the gearbox,the engine or the rear wheel bearings !

Cheers!
Phil

Hi Phil,

I was hoping for an answer like that Hopefully it's just "normal operation", which I'm fine with - just kind of surprised me once the sound of the exhaust system was removed.

Mark.

[DRACO A5OG]

Take a Video clip of it and post it. Will let you know if it is normal or not.

[markmalin]

Will do. Thanks! Forecast calls for rain the next 3 days, so it may be a while, but I'll post it when I can.

Mark.

Originally Posted by DRACO A5OG

Take a Video clip of it and post it. Will let you know if it is normal or not.

[FrinkFrog]

Everything you describe about the sound and where it's coming from was exactly like what I encountered when I first got my SC. It turned out to be a bad passenger side rear wheel bearing... and at 130K miles.... it made sense as well. Now I'm waiting on the driver's side. I'd still try to make the video by having someone outside of the car as you drive down a quiet street.

[wildcat077]

Like the boys say ...
There are people on this forum who've seen and heard a lot more "noises" than we can imagine so by posting a video someone will pinpoint it right away !

Maybe it will be the same mystery noise i've been chasing

Cheers!
Phil

[slw911SC]

Mark:

I hear noises every day - and I don't think I'm crazy? Or am I ...?

It could be:

Wheel bearings (like someone else said). Load up a left/ right hand turn and see if it gets worse on either rear side. Could also be fronts. They would be easier to determine.

Main fan bearing. That would be whiny!

The engine bay fresh air/ auxiliary fan. Sometimes mine just doesn't shut off off at all, and whines away out back the whole time the car is running.

The front fans?

The air filter. Believe it or not, when I installed a K+N filter, it made a heckuva whining metallic racket (almost screeching) when the box was sucking air in. I changed it back to paper, and the noise was diminished.

Tire noise. I just changed a set of Avons that were unbelievably whiny.

The neighbour's cat!

[dshepp806]

Originally Posted by slw911SC

Mark:

I hear noises every day - and I don't think I'm crazy? Or am I ...?

It could be:

Wheel bearings (like someone else said). Load up a left/ right hand turn and see if it gets worse on either rear side. Could also be fronts. They would be easier to determine.

Main fan bearing. That would be whiny!

The engine bay fresh air/ auxiliary fan. Sometimes mine just doesn't shut off off at all, and whines away out back the whole time the car is running.

The front fans?

The air filter. Believe it or not, when I installed a K+N filter, it made a heckuva whining metallic racket (almost screeching) when the box was sucking air in. I changed it back to paper, and the noise was diminished.

Tire noise. I just changed a set of Avons that were unbelievably whiny.

The neighbour's cat!

+1 on all of those!

Doyle

[nesslar]

Wheel bearings get my vote. Been there. Not in the 911, of course......it was a Fiat
People have loud exhaust systems so they can hide all kinds of noises; wife, GF, kids, mom-in-law, rods, bearings, tires, neighbors, cop sirens, rap "music".....

[equality72521]

I have a whirring sound from the rear too. It turns out it's a turbo.

[markmalin]

Gents. I finally got around to videoing the wirring sound coming from the rear of my car. It's faint, but hopefully you can here it. Note, this was filmed while "coasting" to a stop in neutral.

Some additional notes real quick:
- It's intermittent, it doesn't happen all the time
- Seems more likely when the car is hot, though not always
- Seems more likely to start after about 25 miles, but not always
- clutch in or out, in or out of gear
- stops about 20 mph, starts back up about 30 mph

YouTube - ‪IMG 0645‬‏

[jrolstin]

My first thought also would be wheel bearings. A quick way to know for sure is if it changes during cornering (under load). If it's a wheel bearing it will get louder with some weight on it. ex. louder on a right hand turn is the left wheel, and left hand turn would be right wheel. If it's not that it could be a CV joint, peel the boots back to see if they are still packed with grease well or not.

[markmalin]

Doesn't seem to change under load (turning left or right). I tested that and it seems the same, but may try again.

So to check the CV joints can I just peel back the boots, as you say? Any advice on how to do that, or just peel them back?

[Ken911]

The thing is about wheel bearings I had one go bad. The sound seemed to be coming from the the front of the car. Actually turned out to be a rear wheel bearing. So make sure when you check the bearings check them all.

[jrolstin]

Another way to pinpoint bad wheel bearings front to back and side to side is to pick up the car and get the wheels of the ground. Go around and check for play by putting one hand at the top of the tire and one at the bottom and wiggle as if you are trying to change camber. If you get play from this, even the slightest amount, then your wheel bearing is beginning to fail.

[kach22i]

Originally Posted by markmalin

YouTube - ‪IMG 0645‬‏

I've have same sound and symptoms (right rear), please let us know what you find.

I'll do what jrolstin suggests next week when I have the time.

[paulo]

Hi Mark,
Just went through this with my 1989 Ruf CTR. Spent two years listening to a whining noise from the rear. Starts after I have driven about 15 km., no change whether the car is in or out-of-gear, clutch in or out, motor off completely (no fuel pumps on) and coasting at 100 km/h, no change when I jerked the wheel left to right. Wasn't the rear wheels bearings, not anything to do with the rotor or caliper nor any interference with the emergancy brake mechanism. Was not the fuel pumps (three of them) or the cooling fan.
It was the bloody tires! As soon as I removed the Ruf wheels with Goodyear Eagle F1s and installed a set of Porsche wheels with Michelin tires (same sizes) the noise disappeared.
I was ready to authorize a gearbox overhaul when the real problem was discovered.
Not saying that tires are the source of your "whine" but try another tire brand to be sure.

Paulo

[jrolstin]

I agree with Paulo, it is possible it can be your tires. Another question is does the whirring change frequency (increase) with wheel speed? If it doesn't then it could be the fuel pump.

[jrolstin]

Try to isolate it to a category engine / suspension. Is it linear with wheelspeed or is it linear with RPM. That is what I was trying to say above. It will help us troubleshoot.