THX sound

It helps to know that a crescendo is the loudest point of an increasingly louder sound. Given the context of the rest of the song, I can only assume it’s a woman screaming or the window he (the smooth criminal) came in through breaking.

The lyrics specifically say:

As he came into the window

He didn’t come “through” the window, but rather “into.”

So one would have to assume the crescendo was the loud groaning sound the smooth criminal makes as he empties himself on the window.