Jim---Chances are it's just the internal cable that has used up it's
supply of assembly lubrication. It's easy enough to disconnect the tach
at the back of the instrument and pull it out. Coat the cable lightly
with your favorite grease, as you feed it back into the outer sheath.
If your car is not road-worthy, you can then test the cable by inserting
the square drive end (at the tach connection) using a drill motor. IF..
it's like the speedo, you'll need to use the "reverse" mode of the drill
to get the tach to turn. Using the drill motor will eliminate the tach
drive itself, as a possible cause ot the sound you heard.
In some situations, the outer cable sheath can be so badly deteriorated
that even adding lube to it won't stop the noise. Sharp bends in the
cable is one of the reasons for wear. Only a new cable can cure this.
They're about $15 or so.
Dick
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