There are a couple of reasons as to why your Gimbal may vibrate. To eliminate this, try these:
1. Recalibrating the Gimbal sensors usually helps best. Please refer to this article to learn how to do it - http://help.airdog.com/article/33-camera-gimbal-calibration
2. Make sure the Gimbal cable isn't limiting Gimbal movement. This screenshot should help - http://screencast.com/t/mb5awO9FS
If these don't work, contact us and we'll be at hand to help.