I don't know what level of electricianness you have, and didn't want to sound patronizing by asking if the GFCI's are actually rated for your purpose. (I have seen some people quite innocently plug 50A units into a GFCI made for small appliances) The way you've descibed your issue, it sounds like you are somehow connecting the power without a ground and all is fine until you ground it. Without any visualization of what you are describing, I am unable to begin even guessing.
Please, some more technical details. I believe brewing beer is one of the great priviledges of living and don't want to see anyone denied that over a technical issue, and will help if I can.