Nissan Repair: 93 maxima, rear valve, valve cover

Question
93 maxima with ve30de engine has knocking or tapping from rear valve cover , but it doesnt do it all the time when you first start and drive it doesnt knock until driven for a while then it will start knocking ,but then it comes and goes,have put engine and ihjector cleaner in it but didnt help any ideas on what it could be

Answer
Probably a stuck valve dampner.  Change the oil and see if it goes away.  If it does not remove the valve cover and check to see which one is ticking.  You will probably have to remove the cam and replace the dampner if it is beyond specification for tolerances.