When on initial climbout, when my ASI is at 85MPH it will briefly start violently swinging back and forth from around say 75MPH to 95MPH. This only happens when im climbing out and doesnt always do it, but most of the time it does. I can lower the nose a touch and with a little bit more speed, say 87MPH it stops and it does not start doing it until it gets to 85MPH. I had my pitot static test done a few months ago and they didnt find anything but I dont think it was doing it then. Suggestions?