The metal pushrods........

It's nice to have the stiffest rods possible, but flutter most often comes from slop in the connections. Next comes flex in the connections. So even with metal rods, make sure the clevis pins are a close fit in the horn's holes, and any threaded parts fit tightly. Very often, you'll see threaded clevis that are loose on the threads of the pushrod. That's asking for it.



.