[amsat-bb] G-5500 and LVB tracker question.

I have the G-5500 and a LVB Tracker on my antenna set. I have noticed that when the pair are just setting there the LVB tracker will loose its place. By that I mean if the G-5500 box is at 180* the LVB will start out at 180 but as it sets there it will soon be at 178, 174, 172 and so on. I also noted the meter on the g-5500 is going down too. Where do I start looking ?

Marv N0FJP