I also can't get a handle on the controls. I just unlocked abilities that tells me to press ctrl when I'm about to land, and another that makes my legs go crazy by pressing space. When do I use those abilities? Also, how to decide when to slide or jump over an obstacle?
I don't think you can disable only that song without modding.
My recommendation is to change your controls so the soft landing is Left Shift rather than Left Control -- your hands will thank you.
To use it, HOLD the key when you're about to land, and you'll do a soft landing. Once you get shift (Right Click), you can soft land and then immediately right click to fliproll out of the landing.
About sliding or jumping, do whichever you enjoy more. If you're looking for every second on a time trial, always coil jump instead of sliding, as long as the obstacle allows it.
About your legs, that's the coil jump -- it lets you jump without losing momentum. Jump and press the coil key whenever you're jumping over an obstacle or running off a ledge, if you're looking to save time.
*edit* Also, coil jumping means you don't grab onto pipes, ladders, ledges, cables, etc. This can be useful sometimes.