I have been trying to find a solution to this for a while now. My problem is not low framerates, but choppy-ness. When running around the framerate stutters inconsistently. My framerate is buttery smooth when standing still, but the second I start walking the game starts to stutter. No other game exhibits this sort of issue, so it is not a background software issue. Also my settings for the game are on high, which should be rational for 2 6970s. The choppyness is there when I disable crossfire as well. I hope someone knows what is going on.

Specs:
i5 2500k @ 4.5Ghz
2x 6970s @ 985mhz (water cooled)
8gb of DDR3-1333
Win 7 64bit
Latest video card drives and CAP profiles

It's your HDD imo. It can't stream the data fast enough.

Stop other programs that might use your HDD (i.e. utorrent) and install the game on one that doesn't have Windows on it. (just to be clear, I mean a physically different HDD)

Or if money allows it, get an SSD.

Didn't happen to me in this game, but in Deus Ex: Human Revolution. Actually, a lot of people complained about that - new rigs, up to date, almost no problem running it in DirectX 11. However, at some point, in order to improve the stability, I (and others) had to switch to DX9 (and TW2 is a DX9 game). And this is what happened exactly - stuttering when walking, especiallly when turning around. Apparently it had something to do with the way the GPU managed the textures (a patch came later and fixed it, somehow).

I have almost the same specs, except for the GPU - mine is GTX570. I'm no programmer, so I can't really suggest a fix, but from my experience, other than checking the HDD speed, as suggested, I'd also check the DX9 Runtime library and make an update, or repair it if necessary. Checking/changing the sound board/chip settings may help, too.