Just wanted to share my experience and quasi-solution as I have been following all of your experiences/solutions.
I got a MBA back in June and have been experiencing the same problems. I have been hesitant to take it to the store because (1) my particular store isn't always the greatest (I prefer my hometown store) and (2) I keep seeing on here that people are getting the run around.
My experience: Crackling on YouTube, Hulu, and Netflix but not in iTunes or other non-internet based apps. I use Chrome but it would happen in Safari as well. When I took it into the store the problem could be replicated without problem and the audio would actually go out completely.
The quasi-solution part (1): refresh every time it crackles. This doesn't work, genius. (Yes. I said this. No. It wasn't appreciated.)
Quasi-solution part (2): Download Firefox. Because this is only happening in Chrome & Safari, both of which are based on the same platform as browsers (webkit - I'm sure someone else can explain this - lost on me), maybe Firefox will fix it.
"Apple is aware of the problem and they are working on a solution." - courtesy of the genius (Dennis) at my store this evening.
Firefox is a good work around. I don't have the crackling sound anymore. Annoying, but worth it until they fix it. And hopefully this information will give them a look into what it is about the "webkit" base (do I have that right?) that is causing the sound distortion versus whatever Firefox is based off.