Pinging sound when i turn car on and accelerate

Hey all. Need some help. When i turn the car on and start her up, she pings everytime. Its a 97 civic w/ 117k on it. Its been doing this for a while now, 9 months or so, but now i wanna sell the car so i need to get rid of the sound. I put new plugs in a while ago, so i know its not that. What could it be? Rotor? I dunno, any help is very much appreciated. Hopefully its an easy fix. Peace