I found out what was causing part of my vibration problem on my 01 330xi. I decided to change my trans fluid as the car has 100k on it and it hasn't been changed. (BMW claims its a life time fluid :lmao so I drained the fluid, and of course as I expected it was ridiculously dark, luckily no metal though, so I took out the old filter, put in a new one from BMW ($100) and put on the new gasket, refilled the trans, it took approximately 6.5 qts. Seeing as how it was a GM trans I put in Dexron VI full synthetic. I did notice that my trans mount was starting to crack, so that will be getting replaced in the near future. All around the job took about 45 min, but thats because I work at a shop and put it up on the lift. It'll take longer if you're doing it at home. I think what happens is that over time, the trans loses some of its fluid, and that can cause part of the vibration that is really hard to track down. Changing the fluid won't make it go away, but will definitely make it less severe, at least in my case it did. I think that the trans mount should take care of most of the rest of that vibration.