AVS Forum Addicted Member
Join Date: Jan 2001
Location: upstate NY
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Unfortunately, your descriptions of the symptoms suggest to me that there might be a problem in the part of the power supply providing power to the preamp inputs of your receiver. Perhaps some of its filter capacitors are starting to fail.
One thing you might try is to short-out the inputs on the receiver that you don't use. I.e. put a jumper wire between the central socket and the surrounding metal of each of the RCA jacks. You might be able to locate some RCA shorting covers at a local electronics or audio/video store. If the hum is being caused by RF interference being picked up by the receiver's internal wires connected to the preamp circuits, this might help -- it forces the input signals to be 0 volts.
Marantz SR7009 avr + MM9000 amp --> Atmos 7.1.4
Fronts=NHT 2.9+AC2, FH+TM=DefTech PM1000, LCR+TM amped