The 6990 is a fine example of pushing the envelope of what is physically possible with current GPU technology. It is difficult to quantify what that must sound like, but I'm sure it's necessary to cool the card down properly. It's just sad that is comes at such a high price.
Now, look at where the GTX 580 is compared to the 6970. If the GTX 590 is truly 2 GTX 580 cores, then guess what's going to happen?
My guess, is that the GTX 590 will be just as loud if not louder. That's just unacceptable from both companies IMO. They need to find a way around this, or they don't need to be releasing something this powerful. The technology is simply too much for our current market.
Has anyone found a video of the 6990 @ full load? I'm currious to see what all those decibels really sounds like.