I finally got a chance to pull my Phantom out yesterday after a long winter. In the fall I noticed that the Phantom wouldn't hover in place. It would go in circles - getting bigger and bigger (is this the toilet bowl effect? Or the opposite of it?). Yesterday I went through a few batteries and each time I would take off and let it hover, but it wouldn't stay in one place. After a few minutes of flying around, it seems to straighten itself out and will hover in more or less the same place. Before I took it out yesterday, I did an advanced calibration in the assistant software and the gyroscope, accelerometer, and compass numbers are spot on. Any suggestions as to what I can try to sort this out? Should I replace the compass? My props look ok - but maybe they're causing the issue? Could it be a GPS issue? I'm just not sure what else I could try.