yeah well one thing is certain, it is not suppose to make that noise.
You say you can adjust how loud it is so its obvioulsy coming from the speakers (that would make sense atleast
). it could then either be strong electromagnetic interference, like for example when you hear speakers crackling when your phone nearby is recieving a text etc.
Or it could be a faulty speaker.
I recently drove under some powerlines and my MBP aswell as iPad and iPhone starting creating weird noises from their speakers when they were in my bag.