Sorry for the thread revival.
I've had this same issue recently with my E46 2005 300D Manual.
The centre bearing and front bush have both been replaced. The propshaft has been phased and balanced by a company in Pretoria called Isazi Propshafts - but I'm still suffering some annoying vibration/humming after 120km/h.
I'm considering having another shop remove & rebalance my propshaft to try sort the vibration out before looking at replacing the prop.
Any recommended propshaft shops out there?