I thought I would let you know that I'm having a similar problem. I've been having center channel audio drop outs and random center channel popping noises with the 990. No burning smell, though.

However, I've gone the route of the online tech support. They had me swap some connections that caused the drop outs and popping to come out of the left speaker. I guess they were eliminating the center speaker as the culprit.

I reopened my support ticket, and expect to hear something this afternoon. So far, tech support has been good to deal with.

I'll update when I hear something.