I think it's the sound of machine gun shooting if you move non-stop. Snake looks shaky when it's moving, I guess it's due to the grid movement, do you put the last segment in front of the first one or move every segment? Also I tried it to play it again right now and got stuck in the upgrade selection menu, clicking on "Get" button doesn't make it exit. I missed what led to it, cause I got distracted, so can't help with this one, sorry.