[Pete in Michigan]

When I got my dad's Model "A", it had a metal to metal grinding sound that was caused by the " Throttle Control Assembly" pivit arm rubbing on the bottom edge of the firewall. Replaced assembly, noise gone.
Another vibration at certain RPMs was caused by a hood rod nut that bottomed out before being tight to the bracket at the firewall. Make sure nothing is loose or rubbing on firewall. The firewall is like a sound board in a piano, it amplifies noises.