Buzzing engines
I'm not a jet engine designer or mechanic so forgive this question if it is naive.
What causes the loud buzzing noise that one hears from some jet engines, particularly at take-off and high throttle settings? It seems to occur especially in recent-model, large, high-bypass turbofans, like, say, those of a 767.
I'm guessing that it has something to do with the front fan and blade speeds getting close to the speed of sound, but I don't know if that's on the right track. In any case, I'm curious about the specifics.