Last trip out, started making a strange noise. Went through everything at home. Changed oil, no metallics. Changed lower unit fluid, very, very, slight metallic look, no water. This was the first fluid change. Changed the fuel filter....no chunks of debris. Pulled the prop off, which just got changed out a couple outings ago, saw nothing out of the ordinary. Decided to take it back out, and see if it was still there. It was.

The sound is like, if something were spinning, and was out of round, and rubbing against an enclosure. A constant rhythm of rub, and no rub. Does it in Forward, neutral, and reverse. Thought it may be an issue with the stator, as my cranking battery just took a dump on me today, but turns out the battery is just faulty. Also, won't make the noise with muffs on, only if it's in the water with the load against it. Or, maybe the exhaust is covering it up. Sounds like it's coming from the upper end of the motor, not down low. Going to take it in tomorrow, as it's under warranty, but anyone have any noise like this before? Just curious.

I bet some smart alec is gonna ask what the motor is.........

It's a 2020 Merc 50hp Command Thrust, should have probably put it in there anyway.

Did this start about the same time you changed props ? Check spacer and hub .

2nd trip out halfway through, yes. Already pulled prop, and double checked it. The only way to mess up one of those torq flex hubs is to not seat it together all the way. And it's completely seated. Same amount of play the prop had when the motor was new. Also makes the noise out of gear.

We can check it out for you

Prop thrust washer may be installed backwards.

Installed according to the directions in the replacement prop, and exactly like the one that came off. Taking it to the shop tomorrow. Don't know how they will test it , they're going to have to get it on the water to hear it.

2 weeks likely before they'll be able to diagnose it, but dropped it off today.

Where you drop it off

does it do at all rpm and speed ranges or just around idle,etc.

and if you have a sst prop.. and the noise is around idle and slow speeds.... its in the gear case and is fairly normal.
mercury recommends the flo-torque iv hub kit, which acts as a dampner at low speeds. (absorbs the shock due to the weight of the sst prop)

They already got it diagnosed, apparently when we dinged the prop, shaft took a lick as well. Seems strange that after changing the prop, the vibration stopped, and the noise didn't start until the second time out with the new prop. But, oh well, guess that's the way it goes. New prop shaft, some sort of clutch assembly, and a new bearing, and it will be up and running again. Might even be out before next weekend. Those prop shafts must be extremely delicate, prop looked like it was a very small lick, and not even dead on, just barely caught one blade. Rest of the prop looked mint.

All the time. Has an aluminum prop, and it has the flo torque hub kit as well.

Odd that the aluminium prop bent the steel shaft. Normally the aluminium props prevent such things I knownif can happen, but you say the prop barely has damage. Strange.

If I get the prop back, I'll post a pic. It's literally ridiculous how little damage there is.