Unplug the Cat5 cables from the router temporarily and see if it goes away. I found that in my house the cat5 is radiating from the router and the antenna is picking it up. My antennas are on my roof, directly over some long Cat5 runs. I've gone through 3 or 4 routers trying to find one that is a little quieter. I've also found that devices attached to the other side of the coax (switches, DVRs, Xbox, etc.) can also make the problem worse. I've tried numerous methods to try and filter it out at the rig to no success. Good luck...