Can't say I've ran into similar issues with a dual GPU setup. I have a 5970 and it runs very cool, relatively speaking of course for such a powerful video card. Usually hovers around 70 C with fans on auto. About the same as the 5870 I used to own. That's under a real world gaming situation, not stress tests or anything like that. I barely hear the card when in idle and even while gaming there is only a faint audible sound. My CPU fan is louder, in fact.
The GTX480 may be a different story however.. I've seen a few videos that show it averaging in the high 90s under an SLI configuration.