It could be your drop line, or a corroded splitter hiding under the home. Before I chnaged providers the tech went under our house and discovered the bad line and corroded splitter. This sounds like a signal issue, as mentioned by your techs. I'd reccomend you go down to your local xfinity store and ask for a higher level technician who can actually fix the issue. It might also be the ground block going bad introducing FM noise into the line. This is from experience.
I'll await your reply.