Never seen this personally in the 2 'Birds I've owned. Assuming you've checked that your oil level is correct I would......1. Make sure the wire on your oil pressure sending unit is clean and tight. 2. See if it stops after replacing the oil filter during next oil change. Sometimes a faulty oil filter bypass or spring can contribute to needle flutter. At any rate be sure to report back to the community your findings and results.
It was more than I recall, but I don't recall much! Some good ideas from Brian. If the sender unit is old or unknown it wouldn't hurt to change it anyway, they don't cost much.
Then the old tachos are the opposite, vague and delayed.