The Dancing Gauge...

My oil pressure gauge "dances", or should I say has a siezure. (Usualy) when I'm idling the needle will stay at 40, but when I touch the throddle it jumps up past 140 and will quiver there for a moment before plunging down to 0 and back up and down and up and down and up and down... While it does this it makes an annoying clicking sound. I've tried to get a video of it on my phone, but the steering wheel is in the way and the video capture isn't fast enough to see the needle. Does anyone have any ideas as to what is going on?