We measured the noise of the Sapphire HD7950 MAC Edition with a sound meter around 4 foot away from the closed case. Both when idle and when playing Serious Sam 3 BFE, one of the most intensive games currently available on the platform.
Our sound meter is limited to 28dBa, so achieving accurate readings below this is problematic. In real world terms both cards are quiet, although the Sapphire HD7950 MAC Edition is slightly louder under load, slightly audible when tasked with a demanding game.