I have been getting a screeching sound while motoring. I just bought a 2001 Catalina 310 and had to motor 6 hours and it made the sound once. Yesterday I motored for about an hour and it did it 3 times. I was cruising at 2000rmp and when I cut back the throttle, the sound stops. I then increase the throttle and it is fine. It almost sounds like the propeller is slipping. Could this be a transmission problem? Thank you.