there is a pinging sound from the back side valves could this be the valves.
engine has a pinging sound on 2000 Ford Taurus
The engine has hydraulic valve lifters so they are not adjustable/adjust with engine oil pressure. Your engine has a "knock sensor" which should retard (to some extent)the ignition timing if you got bad gas. The noise could be many things hard to guess without hearing it first hand. Best get it checked in case it can cause possible engine damage.