Tubine Whine

[PITBoat]

We got some videos of the boat today, and it's got a whine that's apparent after it passes. Can't hear it in the boat. Sounds like a vacuum or a turbine engine. What might that be? Doesn't sound bad, I'm just curious.

It's fairly loud too, with the flapper cap only and no exhaust bellows. Maybe it wouldn't sound much different coming out the prop though. It's good at any rate.