OÃr and escuchar deal with the sense of hearing. And just like ver and mirar they are different aspects of the same thing.
OÃr, according to my dictionary, is to perceive sounds with your ear, to hear.
Escuchar is to apply your ear to hear, to listen.
My dictionary also cautions not to confuse oÃr with escuchar and not to use escuchar for oÃr.
If you just hear the noise, it’s oÃr, but if you listen to what the noise is saying, it’s escuchar.