I have two McIntosh MA6300, which I got with a year of difference. The first one, about two years go, presented exactly the same problem. I checked everything I could: Cables, contacts, AC power, etc., but nothing resolved the problem, so I decided to bring it to my technician (in my country there is no specialized service for Mcintosh). Then he started to check it and, after an exhaustive revision and changing all the output transistors (which did nothing to the problem), he discovered that the problem was on the relay. He show me the piece: A very cheap relay that got opened and started to fail causing the cutting on sound and the distortion. He substituted it for a high quality relay and voilá! Problem solved. I was a little bit mad because the amp was almost new. About a year later I got another MA6300, brand new, to bi-amplify my speakers, and gess what...It started with the same problem and again, the problem was the relay. It is a shame the McIntosh use cheap parts as the relay on this model. The good news is that it can be fixed. About the sound, well...I sounds very good once you fix it.