350x question

[unregistered]

I am looking at a 350x right now that I may purchase, but there is one thing about it that troubles me. It starts fine but while it is just started you can rev it up a little and while it is revving down there is some tapping in the engine..............sounds like the top end. If you let it warm up for a minute or two the sound goes away. He said that it has a high compression piston, aftermarket cam and mild port job. Other than that sound it runs very good. Any ideas what it is?

[whiteman350x]

A lot of the Honda 4-strokes tap. One of my 350x taps but runs fine.