I hadn't flown my Nano+ for nearly 2 months. I took it out yesterday to fly it where our drone club flies. I repeatedly got annoying beeps from the controller, and a rectangular box, sometimes it was red, sometimes yellow, popped up in the middle of my screen. The message in the box said "bottom" with a measurement in feet. I hadn't seen any such message ever until that time. What is it, and what does it mean. It would go away when I would take the drone higher. Also, does anyone know how to silence the annoying beeps from the controller, for the collision avoidence system? Thanks for any info on these questions.