I am experiencing pretty much the same thing!
Recently built a PC with a Gigabyte 4870 X2 and Vista 64-bit.
I get high pitch noise/buzz from the card when in Crysis and Crysis crashes after about 10 minutes. I am able to play Left 4 Dead but there is flickering and for some reason TF2 plays fine!
I am hoping this is a driver problem and not an issue with the card itself. Maybe someone more knowledge can shed some light on thus for us...
I am going to try switching to basic from Aero.