A place without a background sound seems unnatural to any viewer, who is also a listener. Foley Footsteps, bodysounds and all kinds of gadgetary noise. All kinds of stuff that tells the viewer, that the stuff your seeing makes THAT noise. Science Fiction films need a lot of this by nature. Basically you're creating new sounds never heard before or at least you try to.
Music Can be anything realy.
You can use just about anything to set moods or destroy them. Part of the UGO network .