Jim M.

I'll almost guarantee it's tire noise. The sound changes as the tires wear, always getting louder as they wear down. As we sit in our 928’s our ears are about 2’ from the rear wheel well. The cavity in the doorpost acts as an echo chamber, transmitting most of the road/tire noise into the passenger compartment. This mod cancels out the noise. Remove the rear fender liner(s) that goes up against the doorpost. The area had a thin layer of factory undercoating. I cut closed cell foam to fit, then re-installed the plastic liner and injected insulating foam (aerosol can) through several of the gaps between the liner and the fender well. You MUST use Closed Cell foam, because it won’t absorb moisture like open cell foam. Bugs and rodents won't nest in it or eat it and it has a great temperature range, so it flexes with body movement. On the RH side there are fuel lines and a pressure regulator so I took care fitting the foam and only injected it in the bottom 6". This will allow access to these lines and regulator in the future if necessary. The foam expanded out all the gaps, cracks and holes in the fender liner. After it set up I cut or broke off the excess. It made a big difference in the sound coming into the passenger compartment.

BC

I was in a GTS that had a serious noise from the rear and it was the wheel bearing. Like a "wahwahwahwah" at any speed.

Mrmerlin

if you dont find anything obvious try tightening the CV joint securing screws and the rear wheel bearing securing nuts found in the center of the rear wheels. Also check the rear link pins (lower sskock mounts)and the bolts on the tops of the rear shocks

Nicole

He said he tried different tires, so I'm not convinced tires are a factor in this case. However, I find your noise solution very interesting. Do you have any pictures of what this looks like? Can you still remove and replace the fender liners easily when needed?

soontobered84

Did this just start when you put the new tires on it? (hint hint)

Jim bailey - 928 International

this thread could easily go off topic.....

RKD in OKC

I noticed the noise BEFORE the new wheels and tires. And honestly was hoping that would cure it. With the new wheels and tires the noise did not go away, but has been gradually getting more noticeable.

Dennis Wilson

My silber 78 had a similar noise that I heard at speed, then it started getting louder on left turns. Discovered the right rear wheel bearing was going out. Since this is a pressed in bearing, there wasn't any noticeable slop in the wheel like occurs on the front bearings.

Dennis

Jim M.

It doesn't matter that he changed tires. They all make some noise, especially a performance tire and they all get worse with age and wear. (He's also been doing some autocrossing with the new tires.) While driving our ear is only about 2 feet from the wheel well and a lot of noise is transmitted into the cabin. Sorry I don't have any pictures of the process and yes I can still remove the wheel well liner. Re-reading my post I failed to mention that I put a sheet of plastic on the liner so the foam would seperate from the liner. Worked like a charm and made a noticable difference in the cabin noise level. Try it, you'll like it!

RolexNJ

Or tell him to sell the car and go back to the 944T crowd!

RKD in OKC

Hey Rolex, you ever get that 944 Turbo put together? I'm sure am enjoying driving my 928 GTS.

Schocki

The noise comes at 40 mph and stays or does it fade again at a certain speed?

RKD in OKC

Starts at 40 and stays. The frequency increases with speed like tire noise would, but changing lanes back and forth does not change the noise. I assume tires or wheel bearings would change if I zig-zagged.

AO

I still think it's a wheel bearing or parking brake issue.

Not 100% sure this would work, but... Pop the center caps off and jack up the rear end. With the car in netral and parking brake off, put a mechanics stethescope on the center hub and rotate the wheel by hand. If the bearing is going you should be able to discern from one sire or the other.

But like I said, not 100% sure this would work.