2 Days ago I noticed a light tapping sound coming from under the passenger side rear seat when accelerating. When I let off the gas, the tapping goes away, as well as when I am braking. I have already inspected the rear brakes and emergeny brake, briefly looked at the driveshaft, checked for play in the u-joints, and cannot see or feel anything wrong with any of the above. The sound also dissappears when the wheels are in the air and the car is in gear, but when I manually turn the wheels with the engine off I can hear it from the outside of the car. I plan on pulling the diff cover off sometime soon to grab a look at the gears, but before I do I wanted to see if anyone else has had this issue before.

Any experience or advice would be greatly appreciated.