Take the top off the voltage regulator and see if the points behind the BAT wire are opening and closing in cadence with the chirp. It's possible the regulator settings are wrong and the cutout relay is cycling, causing the belt to slip on the pulley intermittently. If that's the case, the ammeter is likely to spike up and down in the same cadence.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!