So I have two GTX 560Ti cards in SLI mode and do some folding with them. In general they are ok but sometimes especially when I leave the PC running overnight, I notice that there is a strange oscillation on the use of the two cards. Thus normally they are both at 100% usage by the Folding client, during the oscillation one goes to 100% then the other to 0% and then they reverse. This keeps happening ad infinitum. You can see this as spike oscillations in the GPU usage graphs. They are symmetric of course. The CPU client still folds but the whole system (Windows GUI etc) just slows down to a halt. Any ideas what can cause this? It is not overheating I am sure.