my car originally had a 3.1L auto. I had a slight vibration grinding noise under acceleration. I just put the new motor/tranny in, and now the noise is a lot more noticeable. I pulled the rear end cover to check for metal or anything noticeable, and it all looks good. the ring and pinion have a good footprint, no chips galling or anything. I changed the u joints, and the old ones had no noticeable problems. Of course the new motor tranny has new mounts. The noise is not noticeable under casual driving, but when you nail it, it really gets bad. Would rear wheel bearings cause this, or could there be a problem in the pinion or carrier that I can't see. Thanks for any input that anyone wants to share.