That's true; I should've made this more clear. I'm using a "supergun" tool that is designed to lower the level back down to line-level, so I don't actually need the amplifier to run at anywhere near its full capability; in fact, that'd just be a waste. I just need to give it enough power to work at all.

Even so, I wouldn't be surprised if the high-pitched sound you can faintly hear in the video at the end is due to the effect you mentioned.