Mine has over 280k miles, gearbox is pretty quiet. Diff is a tad noisy, but not annoyingly so.
I did note that the 'box got to be quieter after I changed 75w140 gear oil out for full-synth ATF. Shifts better as well, especially in the cold. I have an ATF-label Getrag 240 though. There were three specs for lubes, seems BMW was random about which 'box each car ended up with. Do you have a label on the passenger side of the gearbox housing?