Got this yesterday.
During climb to 5000ft, one altimeter appeared to have lost its damping. The needle wobbled about by about 30ft up and 30ft down. The overall indication was correct.
The other altimeter was solid. The VSI was solid. Everything else was fine. The altitude itself was of course steady too.
Pulling the alternate static produced the usual result in all the P/S instruments but didn't change the #1 altimeter behaviour.
After about 10 mins, the problem disappeared and was not seen again.
I don't know if altimeters contain any fluid damping but if the fluid had leaked out how did it get back in again?
There are two static vents, one either side of the airframe, and left/right yaw made no difference. The two vents are combined into one pipe anyway.
Any ideas?