When I was out with my LSV towing a tube I could yank the steering to throw the tube into a slide out of the wake. By leaning the boat over and pulling around the sound of the boat would change, this is the prop running in the wash off the bottom of the boat which is an air/water mix. Once you put it down the noise goes away.

That is what I found anyway. I filled the center sac and never heard the prop again.

Generally running a prop in air or air/water is bad. At leat that is MHO.

SD2