I'm currently experiencing the audio dropouts that others have complained about with UltraTV. The weird thing is that if you rewind it the audio dropout isn't there. That leads me to believe the ARRIS gateway is at fault. Do my signal strengths look okay?
I would change out the splitter first with a new one that can go up to at least 1 Ghz. If you can rewind it and the picture and sound are both fine then the media gateway is recording it just fine. It's the connection from the media gateway to the media player.
Since the splitter is the cheapest part to replace, replace it first. If that doesn't fix it, call WOW to have a tech come out to test your coax lines and/or crimp new F connectors on your coax lines.