Hah, that happened to me on one of my updates. I kept assuming the firmware update had completely failed because nothing was happening excepting that annoying beeping for half an hour. I kept trying to restart and troubleshoot. Finally, I just put it in a separate room so I couldn't hear it anymore and walked away. When I returned, everything was good. I feel like DJI needs to make it clearer that the firmware update can take a very long time and that the annoying beeping that sounds like an error code is just to be expected.