Wait, what go pro version did you get? Hopefully 5+ with image stabilization that really helps especially on trails. That static crazy sound is from the audio encoding of your raw video into your video editor I assume. I had the same thing in my first video. If you play the raw video on your PC, you will noticed that it is not there. This is all assumption of course so find out the proper conversion into your video editor. Raw video -> conversion software -> video editor