I have a Yamaha HTR-5240 home theater in a box system. It's about three years old. When I am listening to my digital cable music stations (I guess that's the only time I notice), there is somethimes a scratchy quality to the sound. It comes and goes. I have never noticed this when listening to CDs. I have had the cable company out to check the cables (no problems found), but I have not switched cable boxes.

Could the cable box be the problem, or something else?