I'm thinking it is more than likely some component not being able to keep up with the demands of the audio track. Either severe clipping due to driving all channels to max, or just the surround being driven harder than normal, and reaching their physical limit.
Yes, that is exactly what it sounds like...something not able to keep up during the peaks in the audio track.
If it is severe clipping then the speakers are permanently damaged now, because I hear the distortion even when a single speaker is hooked up at a time (and I tried all three fronts & both surrounds), and I hear it even at low volumes.
