[husker boxster]

It could be 1 of several things. I'll list them in order of possibility:

1. Wheel bearing. The right rear wheel bearing from your era (esp 01) was a weakness on S's. With the car jacked up, grab the tire at 9 & 3 and see if you can wiggle it. Then duplicate the wiggle at 12 & 6. A bad bearing will have a rumble when driving that gets louder with speed. You'll hear it if you turn the wheel - it'll sound like rusty marbles when you spin the wheel.

2. Wheels hitting suspension. Are your wheels factory or aftermarket? Aftermarket hardly ever have the proper offset, so they bump on things like the long alum suspension bar. I know you said you've checked for interference, but when jacked up was your suspension loaded or unloaded. Under loaded conditions, it might be scraping something. If you jacked your car up from the proper jack point, your suspension would be unloaded.

3. Emergency brake pads. They reside in the rear wheel hats and maybe there's something out of whack in there.

Or it could be something else.