GTX 480s are loud because of the heat and high power consumption. Owned two of these but I had to water-cool them right away. They were running so hot that lava was oozing out of them... The 600 series are really power efficient and they run super cool and quiet. My 2x GTX 680 in SLI is a lot quieter than a single GTX 580 Matrix I used to own.
My computer runs dead quiet when gaming and its about a foot away from me. I could even hear my wrist watch ticking from 10 feet away lol.
Edit: my case's 90 degree orientation design helps cool reference design cards more efficiently. That could be one reasons why my GPUs are running cooler than normal.
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