Where's this noise coming from?

I would avoid those shadetree guys. Do they drive Chevys? Bad plug wires will cause missing. Look at the engine on a real dark night. If you see flashes from the plug wires, they are old and leaking charge, so replace them. If the plugs aren't wired right, it can make the engine run funny. Check your firing order.

"Knock" or "pinging" is technically known as "pre-combustion" or "detonation". It is caused by low octane fuel and/or too much spark advance, and is usually worse at high throttle & low rpm like going up a steep hill in 3rd gear at 40 mph, hotter intake air, and higher compression. Most cars since ~1996 have knock sensors, knock module, and computer control of spark timing. Some after-market ECU's can control knock on our engines. If running a traditional distributor and ignition, you avoid knock by setting the timing conservative for worst case and maybe buying premium gas.