Solid mounts/welded diff chatter
 

Those who have solid subframe/differential bushings with a welded rear end.
Do you get a lot of chattering on really slow & sharp turns? Like turning into driveways.

Typically when turning your inside and outside tires would rotate at different speeds. When your diff is welded, you prevent this and get chatter, tire screeching, and funny looks in parking lots.

just guessing but the vibrations from the welded diff is probably making the mount rattle or there's just something loose under your car