How is the audio being sent: Three options
1: RF, (Antenna input on TV)
2: HDMI (I am not fully up on this)
3: A/V
4: Optical
Ok, Most likely HDMI (Your question caused me to learn about HDMI)_ this is a fully digital interface, all data is sent digitally encoded and decoded by the display unit (TV).. What I am about to post applies to Optical, Coxial Digital and HDMI
For things to work properly the sender and the receiver must by "in sync" now I do not know the protocol (yet) used by HDMI but Most protocols include some sync info. But if it gets out of sync far enough, Well, you know better than I what happens cause you are expierencing it.
Resetting (Turn TV off and on, or possibly the DVR) should fix.
Two methods of syncing data exchange.. Synchronous and asynchronous. The latter every byte of data contains sync info, Very rugged, but slower.. I think HDMI uses the first.