Freeview broadcast channels on something called muxes - from memory there are 6 of these, and you should find that if one channel on a mux is causing problems, so will the rest on that mux.

If you doa Google you can find all sorts of info - I only know about this when I was trying to find out why I don't get Men & Motors - that whole mux is out of range of my aerial and I'm too lazy/tight to buy a new one.