audio stuttering

[dg44]

I have a new Mbox Mini that I'm using as an interface to send audio from my mixer to my iMac. That is, my mic is plugged into the mixer (using the mixer's preamp), as well as other audio sources, such as CD player, DAT player, etc. I'm using the two-track ins and outs for MBox inputs and outputs. The signal gets everywhere it needs to and all ProTools functions work as they should. However...

On too many occasions, whether I'm playing back audio in ProTools or just monitoring other audio from the computer, the audio will "stutter" and I have to quit everything and restart the computer to get the audio back to normal. It's kind of rhythmic and glitchy. It's driving me crazy and needless to say, it's annoying as hell to constantly have to restart to get normal audio. It's not a matter of having a bunch of programs open all the time. I'm the type who quits apps when I'm done with them and at most may have a browser open and email at the same time. When I'm using ProTools ProTools, that's usually all I have running at the time. So, any ideas what might be causing it and more importantly how to fix it? Thanks.

It's a 2.16GB iMac with 2.5GB of memory, running 10.4.9.