I'd say that it sounds to be at engine speed rather than camshaft speed, but not being able to see the engine running speed makes this a harder call. Initially I'd disconnect the belts to eliminate those, then pull the plugleads off one at a time to see if the noise disappears when any particular lead comes off. It could be the top of a valve guide adrift, which then slides up and down on the stem as the valve opens and closes. It doesn't sound heavy enough for a big end, but could be a small end, although they rarely give problems, and pulling the pluglead on that cyl should tell you. Remove the plugs and see if you can see evidence down on the top of the piston that something has been bouncing about down in there, and see if a small magnet brings anything out. (Now you know where that missing washer from the last job you did is...........
) Look at the plugs while they're out, as the bottom end of the porcelain can crack and fall off.
The ends of the piston rings can break off, and then wear a path upwards to end up with the broken part above the piston. You can normally fish the bits out with a magnet, however the piston (and the bore as well) get damaged.
Listen to roughly where the noise comes from, then put a screwdriver on the engine, with your ear on the end of the handle and move it about until you pinpoint it. (Keep it away from the plugleads......
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Then if you locate it to a bank, or even if not, run it with the rocker covers off.