All sound fades away when Aurelion Sol uses E

Has this occurred to anyone else? I noticed it while playing on Howling Abyss, whenever the enemy Aurelion Sol used his E while not in Fog of War all sound (including champ VO, background music, ability SFX) would fade away and you'd only hear the E SFX and the sound would only return 3-4 seconds after he finished E. Is this intentional?