Driving the boat this afternoon for 10 mins consistently at 25 mph.
Suddenly with no real change in power - there was a high pitched "squeal" coming from beneath the boat - basically coming from the prop drive.
But adjusting the speed of the boat downward - the noise went away.
The noise never starts right away - it takes at least 5 to 10 mins at 25 mph+ to trigger the sound.
If I immediately tried to increase the boat speed - the noise would start again.

Any idea what could be the problem?