Did you ever get it figured out?
I have a DirecTV HR34-700 connected to a Yamaha receiver using an HDMI cable. It's been working great for years and now all of a sudden it's doing what you describe. As soon as you come out of a 30-second skip the volume gets louder and very distorted. It doesn't do it every time, but enough to be annoying. If I change the Yamaha input from TV to something else and back to TV again the volume and clarity return to normal. I never have this issue with any of the other HDMI inputs running through the receiver. It's definitely linked to the DirecTV 30-second skip.