F3 sound distortion problem

My F3 box has started having sound issues. After so long the sound distorts and it sounds like a bunch of Daleks have invaded it if I change the channel and then put the channel back on its fine again. Not bothering me too much but its peeing the mrs and daughter off lol and it could be a problem once I have sorted the pvr side of the box out

any ideas? Have thought about redoing the firmware but would I lose my channel list and settings?