this does sound like your rear parking sensors activating for sure, but (i worked for hyundai) in all the new santa-fe's and tucson autos when you put them into reverse there was a beep purely to let you know it was in reverse.... its got to be one of the two of the above i reckon, do you have parking sensors?
the power steering, especially on full lock and especially because most micras have teeny little engines can take quite a lot of power to do so (imagine how much physical exertion it takes to hold a non power steering car at full lock) so it also wouldnt be too strange for your revs to rise by maybe 1-200 rpm when your steering wheel is coming up to full lock
