to hum, to intone, to close, to shut
唫 has two distinct meaning clusters that do not share one clear center: one relates to humming or intoning with the mouth, and the other to closing or shutting. These may be separate uses of the same character rather than a single unified idea.
唫 combines 口 (mouth) with 金 (metal/gold), but the historical reason for this combination is uncertain. It may have originally represented a sound or a semantic extension, but the exact development is unclear.
A mouth 口 beside metal 金: imagine humming into a metal tube to make it resonate, or a metal clasp shutting a mouth closed. The two meanings are separate, so picture either scene depending on context.
For ゴン, imagine a gong made of metal 金 being struck, and the mouth 口 humming along with its deep tone: gong -> ゴン.