Just launched after a week of redoing the bottom paint and shaft zincs. When going back to my marina, I noticed a distinct harmonic, like running finger over a crystal glass. I have a 3 blade prop, cleaned off growth, scrubbed with green pad and alcohol, then applied the Petit prop guard aresol on the shaft and prop. Used the entire can with about 6 coats on all of it. It was a breezy day, so some could have gotten on through hull for shaft and cutlass bearing. Since then, the harmonic happens when engaging the prop, and gets louder at higher rpms. I didn’t push it past 1500 rpm. 

I read another article on this issue, but didn’t see anything conclusive. Has anyone else seen this issue?  Would it be something to worry about?  

Im heading back to the boat this weekend to burp the stuffing box. Can’t think of anything else that might cause it. However, I have not looked for a vibration in the engine compartment to the transmission.   

However, it does sound strongest near the emergency rudder post. 

If some prop guard did get in the cutlass, should it just wear away while turning the prop?

Any suggestions are welcomed.