I have a 97 S10, 2.2L, 5 spd, ext cab with 58K miles. The truck runs fine, but I hear what sounds like a ping or knock from (I think) the engine when I accelerate. I don't always hear the noise under accel, and the noise stops immediately when I lift my foot off the pedal. I don't hear it at all at idle or start up, so it doesn't sound like the piston slap issue I've seen on these boards. If it matters - I use 87 octane and the truck still has original plugs.
Any thoughts?