still pretty new to the e34, have an e12 manual w/3.5, but the 90 535iA which I acquired in Dec. has a sort of harmonic vibration at hwy. speed. It is subtle and if I crank the stereo I don't really notice it but that is not an acceptable "fix". The PO replaced the tranny and driveshaft but I can not vouch for the work or integrity of the parts. So is it probably center support or guibo or are there other culprits within the tranny flywheel area? Thanks
billy