Voiced reading with a full vowel: covers humming a tune (哼歌), low-pitched groaning from pain or effort, and the drawn-out 'hmph' snort. Reduplicates as 哼哼 for a sustained moan, and pairs with 嗯 in the back-channel 嗯哼 (uh-huh).
memory
Mouth radical 口 plus phonetic 亨 = a mouth-sound pitched at 亨. Same phonetic powers 烹 (to boil) - both 'h-eng' family sounds with a long nasal tail.
Left radical 口 - a small open square marking 哼 as a sound from the mouth: a hummed tune, a pained groan, a contemptuous snort. Anchors the vocal-sound family alongside 啊, 哈, 啦.
Right phonetic 亨 supplies the full sound with no drift. Its own meaning ('to prosper, to go smoothly') plays no role here - it is purely a sound marker. Same phonetic appears in 烹 (to boil). The high level tone fits the drawn-out nasal hum.
