I was using OS X Lion, and it started there, now I've upgraded my MacBook Pro early 2011 (already upgraded to 16GB OWC RAM) to OS X Mountain Lion, the problem persists, and it gets worse, I don't know which music I can play that will not pause every 5 seconds.
The worse part is, googling for `itunes pausing randomly' you see people complaning since 2008!!!
Like here: https://discussions.apple.com/thread/1675131
or here: https://discussions.apple.com/thread/2068193
or here: https://discussions.apple.com/thread/2442281
or here: https://discussions.apple.com/thread/3078555
What's Up with iTunes developers??
I'm considering to abandon the native OS X music player.
