I had my barracuda speedo rebuilt at a local speedo shop because of the same issue. They said that bushings inside let the rotating parts wobble and come into contact with each other and make that tingy noise. It was smooth as butter after the rebuild. I actually had one speedo that broke the needle off because of the bouncing.
Travis..

70 GTX project, orig 440-4, 4 spd, track pack, FC7, stripper/street racer special.