There is a solinoid on the front of the engine that makes alot of clicking noise on mine and a few other things in there also that make noise from time to time but I don't remember hearing my injectors making any, having them cleaned would not make them quiet,there are several places that do clean them I have seen them for about fifty bucks for all four and they replace the screens in the top of them that rust out and the o rings. oh ya they will batch check them if you ask them but you cannot rebuild them you have to get new if bad,I think there around 139.0 to 169.00 each.