I was just about to post a similar question. I was visiting the Aged P's and after I clicked on Yes to re-tune their TV (new channels apparently) they got the same problem with all BBC channels. The problem doesn't occur on their other TVs (set-top boxes not in-built digital) and there doesn't appear to be a problem with the signal strength. Bizarrely if they watch a programme they get the problem but if they record it, no problems! Their transmitter is Emley Moor, is that yours? They've rung the shop where they bought the TV but they say it is the transmitter, but I can't see how.