89 sierra engine pinging

my 89 sierra will start to make a pinging or chatter type noise when i mildly accelerate. someone told me it might be the valves sticking .the oil psi is always on or near to 60psi , what could it be and how can i fix it . thanks

If the timing is good check for proper egr operation.

i checked the egr valve and it works good , do you think if i put some marvil mystery oil in, it will help . or anything else you know of. thanks

As maxwedge said, have you checked the timing? If the timing is to far advanced then it will ping. Also if you are running a performance chip and it requires a higher octane gas and you are running a lower octane it will also cause pinging. If both of these are ok and the pinging is still there you may want to test your knock sensor to see if it is working.