Thanks, guys.

gonk, you are correct. I get the popping even without a signal from the 990. I am running unbalanced connections and the switch is in the correct position. Also, I did swap the center channel interconnect with a known good interconnect in my previous tests, but I forgot to put it in my list. Still got the popping.

Man, I'm dreading sending the 7700 in for service. The thing is a beast. I had to help the Fedex driver carry it into my house when it was delivered.