I bought a very nice refurbished M2A many years ago and it has been exceptionally good to me. I have it as part of my TV surround system driving just the two main speakers. it is housed in a furniture piece with wooden doors. We open the doors to power on the receiver which in turns fires up the amp. WELL...the other day when closing the wooden cabinet door there was a loud 'POP' at the speakers. Upon further investigation finds that if i tap the amp pretty much anywhere with a slight knuckle tap the meter bars will almost spike and a loud pop at the speakers is heard. I am assuming there is a loose contact or connection. any idea what could cause such a thing. Oh and besides that "pop sound" the amp still works flawless.