My 97 Polaris Explorer 500 has always had what I think is a piston slap at nearly all engine speeds, but more so at fairly high speeds. It is most noticeable when running at constant speed or slightly accelerating with the engine running 3000 to 4500 rpm. The Polaris piston probably is a design that doesn't have good expansion control so has to have fairly large skirt clearance. There are other design features of pistons too that have an effect on piston slap. It shouldn't do any harm to your engine, but it sure would sound better without the slap. Al Elston