This is making a ticking/tapping noise and it seems to be associated with my tachometer.

When my tach reaches 10k rpm, the needle seems to get stuck, and then I hear a ticking noise from this unit under the hood (see attached). Its on the driver's side and attached to the inner fender wheel/well. The engine runs fine, and the tach eventually pops out of 10k rpm and bounces back to normal. What is this? How do I fix this?

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1985 300TD Turbo Diesel Wagon
273,000 miles