I would try to isolate the noise down to exactly which driver in the M80, if it is only one driver and not all of them. If it is all of them, it could be you are hearing distortion due to underpowering the speakers. That scene in Iron Man is very demanding and at loud volume levels an avr could easily be driven to distortion.

Jason
M80 v2
VP160 v3
QS8 v2
PB13 Ultra
Denon 3808
Samsung 85" Q70