I have started to hear the Hurth transmission or prop shaft making a high pitched whine when the boat is in forward and the M25XP is running between 1200 and 1600 rpm. It does not seem to effect performance and drops away as soon as the throttle is taken above or below those rpms. ATF was replaced 2 weeks ago with no change. Any ideas would be helpful.
1990 C36Mk1 "PenniMizer III"
Lake Ontario, Sodus Bay NY