I have a 1995 TRX 300 fw that I bought when it was less than a year old. It has been well maintained and treated gently. It will start with a quick push of the button and has good power. Compression is 190 psi and when checking the cam chain there is 3/16" gap between the cylinder and the tensioner. It has an engine noise that has been getting worse over the last 4 years. When it is started cold it runs smooth and quiet at idle, but if you give it just a little gas (1/8" on throttle) it makes a loud clacking noise. If you give it more gas an rev it up it is smooth and quiet. It clacks even louder if you cold start it and try to ride it without warming the engine up. Sometimes the engine will sputter and miss when doing this. If you allow the engine to warm up for 2 -3 minutes at idle it will not make the noise or miss. Even with a stethoscope I cannot tell where it is coming from other than top end. When the engine is completely warmed up, there is a faint tap coming from the cylinder. This engine has never been torn into. I am thinking piston slap, but don't know how to verify this. What do the experts say and what would you do to it?