perhaps this might help you,
http://www.rage3d.com/board/showthread.php?p=1336578119

i had a GTX295 which is a dual GPU aswell, and while FFXIV runs well with 2 GTX460 in SLI it performed very badly with my GTX295.
worst 550€ i've ever spent in my life.

as for your strange noises, can't help you there, i know a few ppl running on 1-2x 5870's and they don't have those problems.