Flickering on STV HD channel

I got an Humax HDR Fox T2 PVR a few weeks ago and have been delighted with it until a few days ago. One night there was a lip sync problem on STV HD but this went away. The next night a random flickering (hard to describe but sometimes like a camera flash) appeared and it is still there. All the other HD channels and SD are fine. I can't understand why only this channel would be affected? The signal quality is a consistent 100%. The transmitter is Rumster Forest and I've checked to see whether there is any transmitter work being carried out and there isn't. I don't know whether it is a co-incidence but the Mux Channel 24 isn't tuning in properly. I decided to carry out a factory setting to see whether this helped and ended up with loads of 800 channels and the usual channels for STV, Channel 4 hadn't tuned in to the correct signal. I carried out a manual search and all these channels are now grouped together under Channel 0. It is doing my head in and don't know what to do? I got this PVR so I could watch HD and STV is the channel I watch the most but it's getting to the stage it's so distracting I don't want to watch which defeats the purpose of getting it. Any advice would be ever so much appreciated.