rear end noise
 

when coasting to a stop, (2000 996 ) in or out of gear i get a distinctive noise from rear that slows or speeds up as wheel speed changes.....it's not a very mechanical sound, rather like a flat spotted tire or something......I can't hear it when going above 20 miles an hour, probably due to increased wheel speed and engine noise...any ideas would be helpful

Check the fluid level.

Find a parking lot, drive both directions in a circle, coasting, see if you can isolate noise one side or the other. That might indicate a wheel bearing. Use the brakes/e-brake on and off when coasting. Might also be a brake issue

If the tread is causing the noise you should be able to feel the tread flaw with your hand.