There has long been thought to be a physiological reason why at least some kinds of dissonance sound jarring. Two tones close in frequency interfere to produce 'beating': what we hear is just a single tone rising and falling in loudness. If the difference in frequency is within a certain range, rapid beats create a rattling sound called roughness. An aversion to roughness has seemed consistent with the common dislike of intervals such as minor seconds.
Yet when cognitive neuroscientist Marion Cousineau of the University of Montreal in Quebec and her colleagues asked amusic subjects (who cannot distinguish between different musical tones). to rate the pleasantness of a whole series of intervals, they showed no distinctions between any of the intervals but disliked beating as much as people with normal hearing.
Instead the researchers propose that harmonicity is the key. Notes contain many overtones — frequencies that are whole-number multiples of the basic frequency in the note. For consonant 'pleasant sounding' intervals the overtones of the two notes tend to coincide as whole-number multiples, whereas for dissonant intervals this is no longer the case.
The work suggests that harmonicity is more important than beating for dissonance aversion in normal hearers (abstract)."