I spent a chunk of my day trying to figure out why Brink kept crashing with "AllocRenderModel Fatal Errors" about every other round I played on my PC, whether in Freeplay or Challenge Mode. One forum thread suggested updating video drivers. I did that, but then the sound got awfully quiet. While alt-tabbed out of the game reading up on this issue, it crashed again, but with a slightly different error (FATAL ERROR: sdMemory::AlignedAlloc). Then I read about a nasty memory leak the game experienced while it didn't have focus (i.e., if you alt-tabbed out of it). Go figure.
While debating how many more driver updates and troubleshooting I wanted to deal with, I decided, just for kicks, to try running it in a window instead of full screen. Red Faction: Guerrilla was nigh unplayable on PC when I ran it full screen (in my experience and one other person I know), but in a window it runs silky smooth. Totally different game, but hey, worth a shot, I suppose. I changed Brink to windowed mode two hours ago and I haven't had another crash or sound problem since.
If Brink developer Splash Damage's forums are any indication, they have their hands quite full with glitches in the game and are chasing their tails trying to find solutions. In lieu of a proper fix, this workaround does just fine for me. And by the way, when it's firing on all cylinders, Brink can be a very good time, despite the lukewarm reception on Metacritic. My hunch is that the rabid Call of Duty crowd couldn't be bothered to make sense of the objectives, teamwork, and class-based gameplay. And, you know, the glitches, though aside from the crashes that now appear to be resolved, I haven't encountered any.
Hope this helps!