So no one else has this type of issue? Ceton Support got back to me and says that they think it's a Windows 7/Media Center issue.
Not sure how I can debug this.
For now, I'm living with it by boosting the volume on the receiver and muting it occasionally if a really loud newsbreak or commercial comes on. I started the process of building another HTPC to replace my wife's DVR. I'll see if I get the same problem with the other machine once all the parts come in and it's built.