You are actually hearing sounds its just that you brain does not know what they are and then classifies them as a noise you hear frequently.
My phone vibrates, then...NOBODY CALLED! OOHHHHHH!! SCARY!
THEN WHO WAS PHONE?
I always heard a Sonic ring chime in every gas station store we went to on our trip to the United States.
I swear i hear the Steam message sound even if i'm not on Steam