Okay, I tried playing Empires again today and didn't hear any crackling. Haven't tried teamspeak. This is definitely a weird intermittent thing, which is why I hadn't returned the board yet, unless this can also be a hardware-induced phenomenon? Looks like tomorrow is zero-hour with respect to being able to avoid having to do a warranty request with Asus.

So, think it's probably drivers? Or more likely hardware? I'll tear it apart and exchange the board if it's hardware, but I have to admit I'm worried the next board might be worse >.<

I haven't had sound problems in other games so far, so I do kind of wonder if maybe HL2 is doing something fishy. I sort of suspect it may be related to having voice chats going on as they seem to really aggrivate the problem. So, it could be that it's having trouble dealing with sounds of multi sample rates (which I think it resamples all to 48KHz per the AC97 spec), but that could still be hardware. It's kind of weird that restarting tends to fix the problem.