It has started happening more recently now, but when I try and tune to ESPNHD, MOJO, HBOHD, etc. all I get is a black screen with no audio. I can go through all of the premium HD channels and nothing. If I tune to a local HD channel that comes in and then go back to one of the previous channels that didn't work they will come in fine. Anyone else have similar problems? My cable company is Cox.