It's on the cylinders on the RH upper side. You can get the Factory race kit one for around $70 or an APE for $50. You have to have the #1 Cylinder in TDC and keep the slack in the timing chain on the tensioner side when installing it.Use the servicemanual when installing it; you don't want to jump any links on the timing chain.

 

speed racer is correct i would believe, the 250's have that as well, i thought it was the valves but the noise was too external, its the tensioner spring that isn't putting enough pressure on the chain, easy fis usually

i haven't checked it myself but this is what i have heard