I thought I heard a number of funny noises when listening to known albums on new M2s, then realized I was hearing things like strings hitting the fretboard, performers clearing their throat, floors creaking as they shifted from one foot to the other...

It's been a year and I haven't found a real problem yet. Followed the M2s up with M60s, VP100 then QS8s.

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8