Weird Audio Lockup / Dropout

Newbie here, so I apologize if I haven't seen the previous threads.

I have a 2011 27" 2.7 8GB Ram iMac. Love the computer, but I have some weird and very annoying audio problems.

When I use Garageband, Soundcloud, YouTube, iTunes or any other media related app, I'll get intermittent lockup of the machine and all audio ceases until the iMac unfreezes (sometimes up to 30 seconds).

Called Apple (I have Apple Care fortunately) and we reset a bunch of parameters, killed some odd codecs, etc. No dice. Problems still persisted.

I lived with it for a while, but I finally had it after I was recording with my buddies and Garageband couldn't push out 4 simultaneous tracks before causing the system to choke. I thought it might be GB specific, but it's anything that plays audio.

Called Apple again and the determined that my hard drive was probably the culprit, and we scheduled to replace it. Well, that is done and the problem is still there - I'm kind of a t a loss now. What could be causing all of these audio related freezes on a brand new hard drive and no 3rd party audio junk to get in the way?

Thanks in advance for any advice.

Get back with Apple Care and make sure you go over with them what has been done in the past with regard to repairs. It sounds like a hardware problem which could be related to the built in audio circuitry on the mother board (logic board). It's something they have to deal with not you especially since nothing on the motherboard can be replaced without replacing the entire board.

Thanks for the advice. I'll call them back and see what they think, but I'll definitely raise the issue of the mother board.