I have the same issue, and the whine starts decreasing around 2700 rpm and stops completely when I get up over 3000. Doesn't do it in neutral or reverse, just in forward.
I have loosened the stuffing box nut off a couple of turns, so it was leaking alot of water, t osee if that was the problem. However it still had the whine. The stuffing box normally doesn't leak much but is never hardly war,m to the touch, let alone hot, so it seems OK.