I've been experiencing this issue for months, now, and tried to find some information online when it first started. Somehow, I missed this thread until today. Upon reading many of the posts, I decided to go back into my Comcast DVR's audio settings one more time to see if I could fix the problem.
I found a way around the issue, but it may cause problems down the road.
After messing with all but one of the audio settings, I was about to give up. The only thing left to try was changing the default language setting. I switched it to Espanol, and suddenly the weird sound was gone completely. Every channel I check still plays in English, so I'm hoping this will prove to be the perfect solution, but only time will tell.
Hopefully this info will help others here, and I apologize in advance if any of your recorded programs come up in Spanish. I guess it's a calculated risk.
Has anyone actually figured out the actual cause yet? I'm seeing this dates back a few years and I still hear this noise and it's giving me a headache. I too thought maybe it was my signal but I was at my aunts house 300 miles away and she has the same issue.