Rivatuner doesn't work, Coolbits doesn't work, nor does the multiple-rebooting method. Other 7800GT cards do/did have the same problem, but they seem to have a different hardware design, with a driver transistor located physically near to the fan connector, which so far as I can see is missing in the black pcb / Molex connector version of this XFX Extreme.
What is more annoying than the fan, is XFX's response to the issue. It seems to be "problem? what problem?" despite vociferous comments over several weeks, and the fact that other manufacturers have experienced problems with the 7800gt reference design. On the XFXForce.com forum thread, there is one posting of "thanks for bringing this to our attention, we are investigating" followed several days later by "we don't know of any such problem". I'm going to give it a couple more weeks anyway, before I talk to Scan and see what they can do. As I said, it's a shame because it's a cracking good card, fast as a fast thing on steroids, nice copper heatsink, VIVO and all the rest.
Memo to XFX: It's not how you fall down, it's how you pick yourself up.
Mike