My new iMac has an odd symptom. The volume becomes softer then restores to regular volume after about a minute. So the cycle is about 2 minutes of regular volume then a softening for about a minute. And this cycle just keeps repeating itself the whole time I am playing something. Its not a wild swing but certainly noticeable enough with narration that I'm just about to reach for the volume control when it magically returns to regular volume. This only happens with the internal speakers. With externals connected or when air playing to the 
TV the volume remains consistent. Anyone else having this issue with their iMac? I'm on 10.8.5
TV the volume remains consistent. Anyone else having this issue with their iMac? I'm on 10.8.5