Do you know the actual QAMs (physical channels) your bad channels are on? It could be ingress from any number of things. I had a bad problem with GSM cell phones messing up NatGeo HD for me.
If you get to talk to a tech (not customer service, but the guy in the truck) ask him if any of the problem channels are on channel 18, 61 or 129. If it's on 129 you're experiencing interference from GSM cellphones. If they're on 18 or 61, it's from VHF/UHF ham radio transmissions. If it's getting in to the cable system then there's a leak somewhere that they need to fix. This can become a problem for them because if they have leaks and any of their channels are on aircraft frequencies the FCC tends to fine them. They have to do a sweep and a fly over test every few years to maintain compliance.
It could very well be that the problem is in your house too. If you have old wiring, all sorts of signals can get in there and interfere.