Browse the net, look for reviews of cards you're interested in. Most of today's reviews have "fan noise" included. Granted, this is often biased but it should tell you enough to know if it's louder than average or not. Generally, looking for ones that have more efficient cooling solutions is best. At least some of them are quieter than reference cards.
I really don't know, maybe someone who is running one can answer your question. I would think though that it wouldn't be because from memory yours has dual fans and this one is a single so maybe it has to work twice as hard?
Looking at some of the cards with dual fans, they're often
louder than single fan designs
. Aftermarket soultions exempted but most people won't go for them as you're voiding your warranty and paying that little bit more on top of the card's price
If it's any help, the fan on Powercolor PCS+ is quiet in idle on a HD4870 so maybe it'd also be for the HD5770 card. With factory settings it's not all that much louder than the rest of the PC. At 25% it's completely inaudible. A fair warning: under load it can get rather noisy.
Anyway, like I said, I'd look for factory overclocked cards with better cooling. Many of them are quieter than normal cards.
