First thing I'd do is unpower and restart it as well as check the HDMI lead (swap it if you have another) and socket (again try another).
Is this Airplayed audio or video material, from the internet (eg past purchases or rentals, or iTunes Match), or streamed from local iTunes.
If it's audio and being Airplayed by guess would be a wifi issue - poor signal or interference affecting the Airplay stream - other playback methods tend to buffer until adequate data is available.
Thanks for your reply.
Here's an interesting development: I fired up the ATV this A.M. and the audio was fine. I had been wondering if there was some type of ambient interference with the Wi-Fi signal last night and, as you suggested, that was probably the cause. This was somewhat puzzling in that there was no problem with the video. I was streaming a movie from HBO GO. Odd: some contributors in this thread said this couldn't be done. I've been doing it since I got the ATV. In fact, that is the very reason for which I bought it.
Well, now the bad news. After running well for a few hours the ATV sound started breaking up again. I dont know if it has something to do with the ATV warming up (it feels only slightly warm to the touch) or the MBP but, as before, the internal audio is fine. I guess it is time to call tech support. I'll try to remember to post a solution here if one is found.
I have been having the same crazy problem. The sound works great for a while then gets fuzzy! I bought my Apple TV 1 week ago. I took it back to the store and got a new one. What do you know, same problem. When does this happen? We rented Dumbo tonight from iTunes and it happened. I switched HDMI cables and TV ports. We watched Alphas via Airplay and Hulu from our Mac Air and it happened again. We watched a Netflix show and it also happened. I have never had these problems with my Roku boxes on the same tv, HDMI port and HDMI cables. What is up Apple?
I know it's been awhile since this post, but just thought I would answer the question here in case someone else is having the same issue, like I was just a minute ago. The break ups in the sound were driving me nuts. Finally, I found this page and one of the solutions completely solved my problem. Most likely the wifi network is overused with the mac and the ATV both using it to send and to receive data and hence the break ups. If you connect your ATV to the router via ethernet the bandwidth is now twice what it used to be with only your mac using it to send data to the ATV. The sound is now as smooth as it gets.
Hope this helps.