As Norman says, electrical work that might have put something else on that circuit or otherwise tinkered with the main panel could be a candidate. I'd also check to see if any wiring had shifted around (which has been the source of hum in my system in two of the three cases I've had such problems - the third was kitchen appliances when the kitchen and home theater were on the same circuit) - the new puppy might have bumped into things and pushed some signal and power cables too close together. Does powering down components upstream of the amps have any effect, or turning off the new wireless router?

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