(Excuse my poor English) Yesterday I had an issue with my phantom. I went in place 5 Km from my house for a flight with a friend which he also has phantom 2 (not vision).We placed the phantoms on the ground, power on, and mine start to flashing red and yellow lights and the dji app showed compass calibration require. My friend has no problems. I calibrated the compass 4-5 times but nothing was changed still red and yellow. I went back to home and I thought I might need to update from 3.00 firmware I have at the moment. Before I update I turn on the phantom but no red light only yellow, I took it outside and yes all was normal with green light. My questions. 1) Is this normal? What can possible cause this problem? 2) Before I power on the phantom I place it on the roof of the car take of the gimbal plastics. Can this affect? 3) The ground was new concrete and I think there is pipe lines under, can this cause the problem? 4) If its on the air is there any possibility to lose compass calibration?