You could try removing the shell of the cooler of your card.
Does that help with cards like the Sapphire xtreme 5830
I have that same card, so I'd be curious about this too. It's definitely a BAD idea to remove the covers for any GPU with a blower style fan, but for cards with a central fan, I don't know. I've also thought about cutting the grills on the vents of my cards that DO have blower fans. Just haven't tried it yet.
Here are some pics of that card:
http://www.overclockersclub.com/reviews/sapphire_hd5830_hd5850/2.htm