like the tapping is comming from the engine bay after i turn the car off. im not sure if it is an issue with the engine cooling system, or if it is something more serous. ive had numerous people tell me numerous things. someone told me that it may be a sticky valve (makes sense). another guy told me that it was my oil pump (kinda makes sense).
my friend has a nissan frontier truck and his makes the same noise after the engine has been running, maybe it is a nissan thing?
let me know what u guys think.

china
ps:98 nissan 240sx, aem intake, apexi n1 exhaust and ngk spark plugs and wires (maybe and issue with any of that shit)

thanks again guys