In my 98 Z3 2.8 5 speed, I get a heavy vibration, almost like a shutter, under heavy acceleration about 3 to 4000 rpm in all gears. Under normal, or mild acceleration, and at any road speed it is smooth. The Tech. at our BMW dealer here is stumped. We have replaced the shocks and links but no change. Now we are thinking it's the center support of the drive shaft. Has anyone experienced this sort of thing when going through the gears, and what was the fix? Thanks!