The problem with testing noise is the condition to do it properly. I have a decibel meter, but I don't have a sound chamber or anything that could test the sound in any meaningful way by isolating it from the CPU fan and other noise. What I can tell you though, is that the fan, even at full load, did not overpower the CPU fan's noise on my test system. Only when I manually set the fan to 50% did it overpower the CPU fan. At full load I never saw it go over 37%.
That sounds better than the 4870 X2's fan. When I had one of those cards in my system it wasn't too bad. Two was unbearable. (The fan speeds had to be adjusted to keep them both cool enough to avoid lockups.)