Ok.. could you tell me which driver your using at the moment? Also have you tried to increase the fan speed on the cards? If you haven't and don't know how there are a number of ways. 1. Download something called 'Ntune', which is a utility by Nvidia and has the option to increase fan speed within it. Get it here:
NVIDIA nTune
2. Rivatuner. This is a great utility for overclocking and other graphical tweaks. It is also capable of controlling the fans with settings enabling you to set up a high and low limit. Get it here:
Link Removed (I use Rivatuner and can vouch that it's a great little utility)
3. I just thought of another option although this is perhaps a little more drastic. The connection lead on the graphics card...