This could be the driveshaft or possibly a broken motor mount. I would get down and check them both.

I would speculate that perhaps you're looking at an engine miss or torque convertor problem, if you have eliminated the exhaust, engine, and transmission mounts as culprits.

does this happen in only cold weather. cause i had the same problem and i took it to the shop and they replaced parts to fix it and i could copy you the list of parts i replaced. mine runs perfect now

Some of the 3 series have what is called a donut between the propshaft and gearbox, these tend to wear and produce slight play in the join.

Couple things could cause this to happen, transmission mounts bad or not torqued properly(16ft-lbs), worn propeller disc, worn drive shaft bearing. Check all those things out to see if their worn.

could be transmission input shaft bearing worn out.