You can start with looking for worn (or missing) transaxle mounts and or bushings, worn CV joints on the half shafts. Any vibrations to go along with that? If so look at the giubos (rubber donuts) in the drive shaft.
I see you're new to the BB. Welcome. Please post a little introduction, and we like pictures of the cars here. Hint hint.
Tech questions like this are best asked in the proper Topic area. For example, the question at hand here goes best in the Milano/75 topic area. All us Milano/75 folks read the posts there.
Again, welcome, and when you find the cause, be sure to report back so others can benefit.