Looking for ideas where this rattle comes from. Kind of sounds like valves that are not adjusted right.

Happens on hot or cold engine
Does not happen when accelerating very slow
Happens is all gears when accelerating fast
Does not happen when idling, nor when transmission is in neutral
Just started doing this about a month ago.
Sounds like it’s on the left side of the engine, but not sure

Adjusted valves, they were fine
All accelerator nozzles have what looks like plenty of gas coming through them.
Thought I got some bad gas(always use 87 octane), but 91 octane made no difference.

Engine is stock 69T, rebuilt 150,000 miles ago with mechanical chain tensioners, original chains(270,000 miles old!), original webers(with air leakage through the butterfly shafts), new Marelli distributor, MSD ignition, never checked accelerator pump quantity, but have never adjusted it either.
Power is no different, that I can tell. Revs to redline just fine. Have pressure regulator on fuel pump and adjusted floats on webers about 2 years ago.

Any suggestions what to check?

My guess at this is an accelerator pump issue since it goes away at 3000 rpm when I think the main jets take over and I need to get a measuring vial for the fuel amount.

Thanks in advance for any ideas
Steve