I'm having the same issue with my DVR-522.
What is happening with mine is that my TV 1 will start to crackle and pop and I will lose audio completely on TV 2. I can restore the audio on TV 2 by rewinding and fast forwarding and the popping will stop on TV 1. This happens multiple times a day and is very random. It doesn't matter if I'm watching live tv or a recording. This all started happening after the last update which added the "On Demand" options.
I called Dish with the problem and they sent out a new 522 which I hooked up yesterday. All was good until tonight and it happened again.
This leads me to believe its a software issue and not hardware. If anybody else is having this issue PLEASE call Dish and let them know. They were clueless when I called but if enough people call maybe they will look into the problem and fix it with a new update.