Corrupted recordings/signal break up on record

I've had my box running for about a month now. Custom firmware etc... Appears to be running well.

I've noticed a problem over the last couple of weeks where the odd recording is corrupting and while it will play back the picture is broken up and very jerky. For example, last week The Apprentice You're Fired was recording on bbc 2, the box was also set to record 10 o'clock live on channel 4. The channel 4 recording was jerky and broken. This week the scenario completed successfully with no corruption.

On Sunday, we were recording Titanic on ITV1 HD and something I forget on BBC 2. We were half watching Titanic and the picture began to break up showing no signal this also appeared to be the case on the BBC 2 recording. Stopping both recordings and rebooting the humax got things going again.

This last Tuesday I watched my beloved blues knock Sunderland out of the cup on itv 1 HD. Big Fat Gypsy Wedding was being taped on channel 4. This recording turned out to be corrupted.
The vast majority of recordings complete fine, but these niggles are baffling me. Am I asking the box to do something it can't?
Where abouts are you ?. Over the last week Freeview reception has been badly affected by atmospheric conditions. Notably in the SE.