cacophonous; harsh-sounding; unmusical
conflicting, contrasting, or contrary; inconsonant, incompatible, or irreconcilable
mismatched, inharmonious, discordant or dissonant, not fitting well together (especially in regards to aesthetics, colors, clothing, or sounds)
adverse or antagonistic; disagreeing or opposing
Producing a clash or series of clashes.
A clash; the sound or action of clashing; violent collision.