I had exact the same thing. I took the amp apart, cleaned it, used allot of contact spray in the unit and the plugs, reassebled the thing and problems solved.
This saved me allot of $$$ for now.

Good luck!

__________________
'01 E53 4.4i exe sport >155K-miles [daily driver]
'00 E46 323i sport >90K-miles [sold]
'01 LR freelander 2.5 V6 >90K-miles [sold]