81 300TD oil pressure gage

[gsamuelson]

Just came back from a road trip and during the ride I noticed something rather odd. After driving for several hours I noticed that when I stopped and the car was idling, the oil pressure gage needle was vibrating, the indicated pressure was normal but the needle was sure vibrating. I could also hear a sort of buzzzing sound from somewhere in the dash. The needle worked fine, lower pressure when at idle and full pressure at higher rpm. The needle would make an audible buzzing/vibrating sound when approaching the limiting peg on the dial face and would stop when finally pegged.

When I reached my destination and the car was left parked for a while the needle would no longer vibrate.

On the way home, after several hours of driving the vibrating needle would start up again, only obvious at idle. Any clues as to why this is happening?