High pitch metal noise when propeller is in gear


New member
Hey guys I would appreciate your advise on what is causing this sound. Bravo 3x, MerCruiser 8.2

I hit some rocks with the lower unit and propeller. Mechanics inspected transom by removing engine, transom plate and sterndrive. A new lower unit and propeller was installed and everything put back together.
We picked up the boat from Marine shop on Friday afternoon and went straight to Lake to test the boat. The test revealed a high pitched whining noise when the boat was in gear when the rpm was raised while we were under way. This was heard when the engine was above idle beginning at approximately 2500 rpm and above. Unsure what was causing the sound, we tested for about 15 minutes and then put the boat on the trailer and took the boat home. (Marine shop at this time was closed since it was past 5:00pm).

The next day (Saturday) I connected the water hose on the sterndrive and noticed that the noise was only present when the propeller was engaged, never with the neutral button pressed (engine only-no propeller) with throttle applied. The noise starts at about 1500 rpm.

The noise is now easier to hear (see video) since the boat is stationary and not going through the water.

What do you guys think the noise is?



New member
Thanks Phillbo for you reply. The Mercruiser mechanic checked the boat out today. The mechanic says the noise is the new OEM lower unit he installed. Mechanic believes the tolerances were off from the factory. Interesting thing was that it took a while to reproduce the sound. It was determined that the gear oil when cold and thick made it hard to detect the noise. When it finally was fully warm, the noise reared its head. The lower unit will take a week to get to the shop, one day to install. I will report back after a very cold test day on the lake. Winter is approaching and I live in the mountains. Wife not happy :)
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Liquid Addiction
Staff member
At least the marine shop it taking care of the issue. I would hope for a test run by the marine shop before you pick it up. Had they done this to start with it would have saved you and your wife some aggravation..