Your problem is not electrical, it is within the cable tv system in your home. Get Comcast back out, have them check ALL of the connectors in the house, on the service drop and at the tap. Look for loose fittings, poorly installed connectors, corrosion between the center conductor and shield and damaged cables. Have them replace anything that is not Comcast approved. Make sure all of the connectors are tight-- a little beyond finger tight (except for the fittings on modems, cable boxes and tv's which need to be finger tight only).
