clinking sound
鏗 centers on a clear, resonant clinking sound, especially of metal or stone striking together.
鏗 combines 金 (metal) with 堅, which likely contributes the sound and the idea of hardness, together suggesting the hard clinking sound of metal.
Metal 金 on the left and hard 堅 on the right: imagine striking two hard metal pieces together to produce a sharp clinking sound.
For コウ, picture a metal gong being struck: the deep 'koh' sound it makes cues コウ, and the clinking metal fits the kanji's meaning.