OK, Thinking-Cap Time...

Jay Honeck wrote:
Of course, we have a new squawk shortly after coming out of the shop.
Perhaps someone here can point me in the right direction?

Alternator problem. Possibly a filter, but my guess is a diode is going bad.

3) The noise slows down -- or speeds up -- in synch with the prop RPM. At
2300 RPM, it's going a bit faster than once per second -- maybe around three
times every two seconds.

Alternator speed depends on engine speed.

5) Adding load to the system (landing lights, fuel pump, etc.) makes the
noise louder. Adding load to the system and then suddenly turning
everything off makes the noise and amperage oscillation go away -- for about
30 seconds. It then returns.

Adding load makes the alternator work harder. Cutting it all out lets it loaf
until the battery charge drops a bit, then the alternator has to work again.

George Patterson
If a tank is out of ammunition, what you have is a sixty ton portable
radio.