REALLY nice catch there. way to go! this is likely a preexisting sample like you said, as this can also be heard in the track "Magma's Danger Room Test" from X-Men Legends.
i'm out of my element when it comes to sample libraries for rock, but if i had to try and whittle it down to where i think it MIGHT come from based on the range of its usage and timeframe, maybe it's in a Spectrasonics CD? i'd have to do some more digging.
very cool :)