Modem causing tv pixelation

When ever there is any activity on my xb8 modem the tv completely pixelates and sound cuts out. With the modem unplugged the tv works perfect. A quick web search shows this is a very common problem. The tech's replaced the coax from the pole to the tv. Ive replaced the cable box twice and the modem 3 times .

I replaced the tv as well. Nothing fixed the trouble. I can't find anywhere on the hundreds of similar complaints where comcast has provided a good fix this trouble.