Have the same issue with my 640d ...
Vibrations at constant speed @ around 1900 rpm and during acceleration ...
Definitely not coming from brakes. Wheels perfectly balanced.
Somehow I have the feeling itīs coming from rear axle drive, drive shaft center bearing or hardy coupling ...
Have not been at dealer yet ... actual mounted winter tyres are on Breyton rims and I know they would argue that vibrations are caused by aftermarket rimes