2003 F225 strange rattle at low idle foreward and reverse

[stripedo]

Yesterday while docking I noticed a strange rattle in my starboard engine when I was at slow idle in forward and reverse. Sounded louder in reverse. Boat ran fine at speed though. Wife said she saw a bit more smoke than normal too. Not sure if that is true

Any ideas?

[rodbolt17]

either its prop chatter and you never noticed before.
or its a slight miss causing the chatter.
or someone did not install the collar and retainer properly at the last water pump change.
those are the three typical reasons for the chatter.