oil presure, could be low or maby switch to slitly different vescosity oil. Or your tappets could be tired . 1 or 2 of mine tap , if there is no loss in performance things should be fine I would think. Maybe check to see if your cam has flatened out. Is there any problem with how the engine is runing? Or having a miss or not reving cleanly? Also hydrolic tapppets do like to tap just for the fun of it, or it may be that your engine takes a abit to warm up and all gets nice and coated. If Lucus products are avaiable to you, try the oil stabilizer, from my own experience the stuff works and works well.
