All of the 5970's run hot. Use MSI Afterburner to adjust the fan speed manually (or to create a charted temperature to fan speed ratio that's a little more robust than the standard settings). I use a GTX 285 right now and I make sure it's always running at 75% fan speed. Before I did that, I used to get polygonal issues in L4D2, but no longer!
Another option would be to grab an aftermarket cooler, but then that voids your lifetime warranty. Liquid cooling is a VERY viable option too, as you can OC the card to a crazy level, but that's only if you're comfortable with doing that. : )