Need help diagnosing a strange noise....
 

Good morning all!

I am making good progress on the 924S project car. Recently diagnosed an overheating issue (thanks to you guys!), so on to the next educational experience.

The car is making a strange noise. It seems to be coming from the rear of the vehicle. It almost sounds like when a semi-truck rolls over the side bumps on a freeway. It is somewhat of a subtle noise - not loud like a semi, and I seem to only really notice it when the windows are UP. The highway speed bump noise will also speed up or slow down with acceleration or deceleration. And then will make no noise when at idle? The noise seems to have a bit of a pattern to it. It isnt a constant drone of a noise, it will be on for one second, off for a second pretty consistently.

Has anyone run into this noise before? Any help would be greatly appreciated. I tried getting an audio clip this morning and the noise was too subtle to be of any help. But I can go out and try again if needed.

I would check the bolts on the axles, the driveshaft coupling Transmission upper mount, Wheel lug nuts, sway bar drop links and shocks. See if there's excessive play in the axles as well.

I'm not a 924 expert, in the least, but as general troubleshooting advice... It sounds like it only happens when the car is moving. Does it stop when you drop it into neutral while moving? If it does, likely drivetrain related.

If not, I'd start by checking tires and wheel bearings. You could dial this in by lifting the rear while in neutral and spinning each wheel to see what you can hear.

Sorry... just got back from out of town. If I drive up to 50 MPH and throw it in neutral, it will still make noise. It will be faster at higher rpms and slow down as the car decelerates. Just got done rotating the tires and checking PSI (30 up front and 36 in rear). Still hear it in the same place. Also the tires do not have play in them when jacked up and the e brake off.

Here’s a much better quality recording I got of it.....

https://soundcloud.com/user-909592178/924s-rumble-noise?ref=clipboard

Wheel bearing.

Agreed...

Awesome. I’m happy to hear that this seems to be a pretty straight forward diagnosis. It’s already starting to get cold outside, and the last thing I want to be doing is throwing random parts at the car until the noise stops. I’ll order some wheel bearings (figure I’ll just do both rears) and report back what happens so that others can learn from this thread down the road. I have the 924S. I understand that I would just need to replace that actual bearing, which looks to be pretty thick compared to the regular 924 wheel bearing?

I agree with the wheel bearing diagnosis.

mine also had a very strange noise from both rear axles, but, on turns it didn't "behave" as wheel bearing. The noise was more prominent on one side.
I removed rear brake rotors and found that parking brake shoes were "sitting" almost at 45 degrees to the rotor - broken hold-down springs.
I don't know, yet" if this was the only cause of noise - the car is still on jack, as I perform other "repairs".
Initially, I though that the noise was from wheel bearing.
I will check for any noises after the car will be ready.