I'm hoping someone will have some advice on this. I have a Marantz SR-9300 receiver and I've recently added two CIAudio monoblocks to the front L and R channels, using the Marantz pre-outs. The problem now is that evertime I switch input on the Marantz (from CD to DVD to Tuner etc) I get a thump through the speakers. This thump does not appear to change with volume changes - it is a constant sound. I also get the thump whenever I change chapters on a DVD or even change television channels (using an external digital tuner box). I do not get the thumping when I use the Marantz's internal amps, that is, it only happens when using the pre-outs. I have tried the monoblocks with a different pre-amp and had no thumping problem. I've taken the Marantz to the repair shop thinking the muting circuit may have blown but they say there's no problem (though I'm not 100% convinced that this is not the problem). Does anyone have any ideas? Could it be the muting circuit even if it only happens with the pre-outs (and the repair shop says it isn't)? Could it be a compatibility issue between the Marantz and the monoblocks (different input/output impedences or some such thing)? Any other thoughts would be gratefully received.