[spiderplant]

This problem happens because of jitter (timing variations) in the Dolby signal broadcast on some HD channels. Although the jitter is within the range permitted by the Dolby spec, not all amps can cope with it.

It doesn't happen with the SA V+ because it regenerates the Dolby timing itself rather than passing it through from the incoming channel. I've not seen any reports of it happening on TiVo either.