To further this line of inquiry are these coming from local channels rebroadcast on Direct TV? (LIL). My local CW at times gets so bad I won't use my AVR for all the pops and signal squeals. Off air viewing is only slightly better on this channel.
One of the pop/squeals forced me to have to disconnect a Yamaha YSP-1000 from power for several minutes and then set up all over again as though new.
The amp overload should be from heat I would have thought but perhaps it is merely protecting itself from a signal level spike. Can you run the amp from say a DVD input for as long a time as your TV viewing and does it pop and go overload?
Is the HDMI cable you connect to the AVR horizontal or vertical in its placement? If the latter could a sound peak jar things enough to break contact on a dangling HDMI connection? Does picture go strange at that moment as well? DUH after reading you use optical to the AVR just as I do. Ignore this question brain popped eyes blinking.
HDMI Breakout box? A splitter? Is it powered? How does it and its power supply (if external) feel? Is it hot?
Don "just some things that come to mind to check" Bolton
The receivers send out a line level signal to the next device.
However, you are getting this pop from 2 distinct different setups which might indicate a problem with the DTV receiver.
Does this happen on multiple channels or just one ?