Hi people i have a s2 rst and the thing is when you start it its fine and no knocking sound then after a few minutes you get a knocking sound on the top end and the thing is when you slightly rev it goes away but when the revs drop back to 1k it comes back but when the engines totally warm the sounds gone. Could it be a wrong grade of oil as im using 10/40w or a knackered cam.

 

Could be worn cam and its fooked tappets as it done it on mine

 

to be honest its my second piper cam in 2 years and if its the cam then its bye bye to piper cams for good