propeller makes banging noise

[trebor11]

2005 merc 90hp 4 stroke. boat has been sitting for two years when it is put into gear it makes a loud banging noise like propeller is hitting something same thing in reverse when in nutruel no noise when i turn the prop in nutruel no noise. what could this be dont know any history on boat

 

[steelespike]

Re: propeller makes banging noise

Perhaps too much end play in the prop shaft or the prop is too close to the anode and end play allows the prop to hit.
Have you examined the prop and lower unit for evidence of damage.
There are anodes designed for these situations assuming the prop is intended for that motor and end play is normal.
Prop nut may have worked loose allowing the prop to slide, may result in a lost prop.