I pulled a 350 tbi engine out of a G20 and took it down to block and heads, I resealed it and replaced most parts but didn't take the heads off or anything. I drove it with every kink worked out, or so i had thought for the first time, a real "drive", aka, to work and for gas. I as listening carefully and could hear a strange sound coming from the engine bay. It sounds like it's coming directly from the intake manifold. A knocking sound, sounds like something hitting something, increases in sound and rate of speed as I rev it. What's the verdict/opinion?

 

exhaust leak?

 

Bad lifter or a bent pushrod, too much valve lash would be my guesses.