Severe audio distortion/noise coming through speakers

Has anyone experienced anything like this before?

For the last few weeks I've been editing along in FCP, not a care in the world, when suddenly an intense amount of very loud audio noise comes roaring through my speakers/headphones/whatever external audio device I'm using. I throw my headphones off and take some ibuprofen, then the problem disappears until the next unexpected opportunity.

It's one of my unsolved mysteries, and it's causing me ear damage.

It only happens in FCP, and only when I'm listening through an audio device plugged in to the headphone jack of my MacBook-- it hasn't ever happened when using the built-in speaker.

Any ideas? Anyone else have this happen? Thanks for any advice.