哗 (huā) primarily represents the sound of rushing water, a crash, or sudden commotion. At huá (second tone), it means 'clamor' or 'noise' (as in 哗众取宠 - to seek cheap applause). The onomatopoeic first-tone huā is far more common in everyday writing.
Left mouth radical - pictograph of an open mouth. Used here in its onomatopoeic / interjection role: the radical signals 'this character names a sound coming out of a mouth,' linking 哗 to the noisy-sound family 喊, 吵, 嚷, 叫.
Right 华 carries the sound huá → huā with a mild tone shift. It is the simplified form of 華, originally a flower; here it is pure phonetic with no semantic contribution. The clatter and crash of 哗 has no flowery meaning behind it.
