Ableton Live sample libraries distorting through headphone jack

So this is a very specific problem that I have just encountered for the first time: I have Ableton Live 8 Suite and several additional 3rd party sound libraries that I use all the time. Last week I showed up to rehearsal with some new sounds and Instrument Racks and when I plugged them in through the PA from my MBP's headphone jack they were all distorted. Through headphones they sound fine, and through my MOTU Ultralite mk3 FW interface they sound fine. I've checked by signal flow through all the routing to ensure that nothing is peaking or clipping and everything looks fine, but for some sounds (sound libraries) they are coming out distorted.

For performance I go through an audio interface for highest fidelity, but for rehearsals and such I've always just used the headphone jack and it has always worked fine.

So heres one funny thing about this, and makes me concerned. Just before i encountered this problem, I had been working on my MBP in my studio. When I went to leave, I ejected external hard drives/peripherals/etc., closed programs and shut it to put it to sleep and put it in my bag. When I got to rehearsal a couple hours later and pulled it out, the fan was going at high speed and it was super hot. Obviously something had hung up and it was working overtime for 2 hours, unbeknownst to me.

I don't know if these things are connected, everything seems to be just fine with the computer - I run Ableton and Pro Tools all the time and haven't noticed anything else funny. Except for this distorted audio on SOME samples. I'm ******' mystefied. I've uninstalled/reinstalled the sound libraries from the original zip files, reinstalled Ableton, checked everything i can check. But it still persists.

Anyone have an idea? Or has anyone had distortion/clipping issues with headphone jack? (FYI im outputting at moderate volume).

MBP Retina 2.6GHz w/ 16GB memory, OS 10.8.2