My 1997 z3 has a vibration mostly in 2nd gear from about 2500 to 3000 RPMs during hard acceleration . After 3000 it smooth's out and doesn't vibrate in any other gear. Replaced center driveshaft Bearing and cushion assembly and universals are tight and Gibo joint looks ok. Almost sounds like clutch or rear end slipping but seems to be under tunnel behind transmission. Any thoughts?