Popping sound coming through speakers

I have a problem with a loud, popping sound coming from my speakers, and then my receiver (Denon AVR-488) shuts off. I have the receiver, an XM radio module, a TV, and the subwoofer all connected to a power surge protector which is connected to a electrical wall outlet. Speaker (for all speakers) resistance is 8 ohms.

I have had this receiver, speakers and speaker wire, subwoofer, tv, and XM for over a year with no problems. I did recently have a new voltage regulator in the receiver installed. I put the home theather back together, and it worked fine for a day. Now, about every 20 minutes to 30 minutes, the sound will pop and the receiver shuts off. I don't have the volume loud at all.

Any help you can provide is greatly appreciated. Thanks for your help in advance.