My 7700 has developed a loud buzz in my rear channels, no audio just a loud buzz when it starts. Every time I turn it on it buzzes, I'll turn off then on again and usually on the 3rd restart the buzz is gone. Then it could play all day without a problem or it can reoccur in an hour or two. The buzz continues with my Marantz 7703 is powered off, I removed the trigger wire and that had no effect. I've had this baby for ever.... bought it new, what to do??? Thanks your advice.

What happens if you disconnect the inputs to the rear channels? Try switching switching the input channels around and see if the buzz moves. Check the cables and re-seat the connections.