My best guess is a bad paper and oil capacitor,I believe Cary may have used them in their products,one or more be leaking DC.I had this issue with a PIO cap in my home built Hagerman gear,I replaced them all with Film and Foil's and this seemed to fix the popping sound I was hearing thru the speakers.
I would contact the dealer/manufacturer and pick their brain.
I would contact the dealer/manufacturer and pick their brain.