I'm in the same boat, but I have found a workaround that might also help identify the source of the problem; please see issue details below.
-XFX HD7950 (FX-795A-TDFC)
AMD Catalyst Driver Version:
-Currently using 12.11 Beta
-Issue was also present in 12.10
-Windows 7 SP1 64-bit, all updates applied.
When not gaming, audio output over HDMI cuts in and out, mostly out. For every 3-4 seconds of silence there will be normal sound output for about half a second.
As soon as I start a game (Skyrim in the present case) the sound performs normally for the duration of the gaming session, then returns to the problematic state when the game is ended.
I haven't yet tried rolling back to much earlier driver versions as the previous poster reports.
Some additional research I did led to the following; unfortunately I've lost track of where I cobbled all the information together that got me to try these things, so apologies to anyone who deserves credit for these discoveries.
1. By enabling then disabling the LCD Overdrive feature in the Catalyst Control Center (under My Digital Flat-Panels) the problem will be resolved until the system is restarted.
2. By increasing the 2D clocks with a manually modified preset (instructions found here: http://www.techpowerup.com/forums/showthread.php?t=117633 ) the sound problem would be resolved entirely, but this also introduced some instability into my system so I stopped using this method. I don't recall exactly what levels I increased the clocks to (though I tried to be conservative), so it's possible there's another value that would have resolved the problem without introducing instability.
-650 Watt, XFX XXX Edition P1-650X-CAG9
-Vizio M370SL HDTV connected with HDMI
-i7 3770K @ 3.5 ghz
Motherboard BIOS Version:
-8gb (2x4gb) G.Skill Sniper DDR3-1600
-Mushkin Chronos Deluxe 240GB SSD for boot and games
-2TB RAID5 (3x1GB HDD) through integrated Intel controller
Issue was also present with a previous motherboard/CPU combo, and HD has been wiped and OS reinstalled with no effect on the issue.