Why do compressors for example in the fridge make that vibrating sound, I've heard a similar vibrating noise in fans which are compressing air as well... i think. Why does compressing air make sound? Can air hitting air create sound waves?
Well you really can't move air without moving parts. (Except maybe a nebula in space being pushed by solar wind?) It is usually a motor and some kind of piston that you are hearing. Sound waves ARE air hitting air, so I'd think that yes, even if no solid objects are involved, moving air would make sound.