Prop noise vs. engine noise

A colleague and I were discussing a plane that has been practicing
aerobatics near his house, and all the noise it was making. I started into
telling him how the prop was making most of the noise, and he seemed to
think I was crazy for thinking that.

I think I will have to show him something written, to believe me. Anyone
know of a website that compares prop noise and engine noise, especially when
it comes to high performance and constant speed props?

By the way I have googled til I can't read anymore!
--
Jim in NC