I think I can here ya KNOCKING!

Did you get your idle issue resolved?

The broomstick idea works pretty good, but I switched to using a long steel rod, like a 3/8 drive extension; it fits better into my ear, and doesn't seem to be affected by my holding on to it. Run it along every intake runner and every exhaust port; Perhaps it's just a lifter or valve lash.
But then, it's hard to confuse valve-train noise with a rod-knock.
Every time I've had a rod go down, I had a dickens of a time proving which one it was, using a sounding-rod.I mean I knew it was a rod,cuz I recognized the sound, but which one? The noise was not easy to pin-point. Valve noises are easy to pinpoint,so, if it ain't in the valve-train or the fuel pump, or crank end-play, well then;Off with the Pan!
Took-a ,took-a, took-a, took-a................somewhere deep inside.