Congrats with the car.. i came from an STi too..
as for the noise, first understand the M is very noisy.. I thought comming from the STi the BMW was going to be silent but that isnt the case..
the car makes a change in sound with the clutch engaged/not in neutral.. as well as plays a melody of sounds while warming up.. and even at a warm idle it sounds very "mechanical" if you will..
no differential sounds like the sti, but it is noisy!
All The M's have that raspy sound and their idles are going to sound different accordingly.. as the e46 m3 sounded "different" than other cars at its idle too..
2008 E92 M3 (03-08-2008-first delivery)
JET BLACK on BLACK w/Carbon Leather, 19's, Tech, 6spd..