If you don't want to swap out the cooler on the 7970 you have then your best option is to go for a gigabyte windforce x3 cards (like a 7970 for example). The gigabytes aren't as good at overclocking as some other cards (duet to limited voltage control it I recall right) but what they lack in OC potentially the make up with cool dressing. The windforce x3 is a very cool and more importantly quiet cooler. Another advantage of the windforce x3 is that its a pure dual slot cooler making it especially well suited for crossfire.
However the stock fan profile is made more for cooling then silence so to get minimum noise the fan profile needs to be adjusted.
Edited by Bit_reaper - 2/22/13 at 5:37pm
For the card in a fully stressed status (in-game) 42 DBA, now that is audible yet not annoying. It means you can hear airflow, but that's it.
Now I do need to add a note here, up-to 60 degrees C the card remains very silent. Once it passes 60 Degrees C, the fans simply start spinning harder and thus start to make more noise.
If you'd be willing to let the card the run at say 70~75 Degrees C and if you grab software like AfterBurner, you can then make a fan profile making the card nearly silent while it remains very well cooled.
That's the flexibility you get with the WindForce cooler here.