I have been hearing an intermittent knocking noise comming from the engine. I had a compression test done and the results indicated 144 psi. It starts easy, runs well at low and high rpm and is not suffering from any power loss. Mixed input indicate piston or rod issues. Any suggestions? I am mechanically orientated, but have never worked on a PWC engine. With the right tools and manual, is this something I could open up and check or does it need a dealer mechanic?