Hmmm. Okay. I just hope it doesn't blow tweeters before then.
If the pop is that loud then time to take it to a repair shop. Thinking if it's in both channels then could be located in the power supply section somewhere. Would a bad cap cause popping? I don't know. Until you get it checked out everyone's reply's will be guesses.
How old is the Sony? When my Outlaw 975 processor wouldn't turn on I had the choice of repair or replace. Technology moved on during the 7 years I owned it so repairing meant I would spend money on an outdated surround processor. New units sound much better. I'm glad I didn't get it fixed and ultimately just tossed it in the dumpster.
Try different interconnects first, they can look good on the outside but the tiny wires inside break easily. Maybe you have wire rats like we do, they love RV wiring.