The outboard looks to have work done to it before I purchased it, new screws around motor, seals, grease, etc. I can start it but it revs high at idle speed in neutral, will go normal for a few seconds then back to loud idle. When I turn the throttle in neutral to higher rev it makes a loud metal on metal grinding/knocking noise but only after I rev it real high and it starts to rev down it makes this horrible noise. It wants to die after all of this noise Im hearing like it has something really wrong with it. What could this possibly be?