Popping when source is switched or muted HUH????

You might consider sending the unit in for an inspection or repair. Popping sounds are caused by arcing 99% of the time in solid state gear - and in your case the arcs are either across the switch(es) or where the soldered leads from the switches meet the pcb. Could be bad/cold solder joints anywhere in that path. The mute function, when activated, "recharges" the arcing process.

Gs, Thanks a bunch! I think I am gonna send it off for a repair, and try to borrow a pre amp while its gone, thanks all!

I have had same pop when a newly modded Tosh 3960 was put into my system.My other sources,a Panasonic dvd player and a Aiwa changer do not do this.I can say with certainy it is the source,in this system.Good luck,Bob