Unstable tachometer

[krazydoc33]

After about three hours of flight time my Skyview tachometer has started to bounce around when over about 4000 rpm. The engine sounds fine but Skyview warning drowns out everything. A loose connection could be the culprit but why only when over 4000 rpm?
Henry

 

[Rhino889]

I had the same issue. Dynon said double the prescribed resistor on the tach pick up line. I did that and the problem went away.