The voltage relay or the current relay are made to vibrate, quite fast actually. They respond quickly and with the long time constants in the field circuit, they provide for regulated current and voltage. The cutout relay on the other hand should not be doing this. If the system is functioning correctly, the cutout relay should close when the rpms are above idle, and stay that way until they drop down. I would be trying a new regulator first. If the PO drove it polarized backwards, that could damage the regulator.
