Bad TV Reception with DVDR615

I have traditional analog cable service with the main coax line plugged into the 615 and the coax out into the TV. Whenever the 615 is on, the reception on the TV goes from a sharp picture to very snowy, with the image barely legible. The 615 otherwise works fine and makes clear recordings. I have gone through the manual and seem to have things hooked up properly. Does anyone have any ideas?