Bio...one note. Mine did that once or twice when I first set it up. It was eliminated by setting each of my source devices to send a specific output, instead of setting them to "Auto" and sending whatever they want. So, for the TiVo I'm sending DD via an optical cable. The PS3 is sending bitstream down the HDMI pipe. The AppleTV is sending DD via HDMI. The Xbox is, well, I don't know because I never turn it on.
It would seem that the UMC doesn't like fast format switches and cut-outs. So, for example, you're on your DVR and it's receiving DD5.1 during a show, then it cuts to a local commercial break and the signal drops out completely for a split second, then might switch over to PCM Stereo, so the UMC is trying to decode 3 different formats over the course of about 30 frames of video, it throws a middle finger in the air and screams. It can be even worse with something like a PS3, which, switching to it could cycle the UMC through DD5.1, no signal, PCM Stereo from the device, DD5.1 because it senses it's in BD player mode, and then the disc itself could switch it over to a DTS format, or a 7.1 format.
I know, most $200 receivers can do this without a hitch, but most $200 receivers don't give you the sound quality you've experienced, especially at the value that attracted you in the first place.
It can be overcome, just lock your sources in on a format they're sending. Make sure you've gone through and told the UMC what format to decode from each input and based on every type of format that could be thrown at it. Another tip is to turn off "10-bit" or "12-bit" or "deep color" mode on any of your sources.
Think of it like the PEQ vs. EmoQ. You could set it on "Auto/EmoQ", but it performs much, much better when you tell it exactly what to do. It gets a little flustered when you want it to make decisions. Just be assertive. It will obey, and it will make you very happy, and you won't be sacrificing any quality at all.