This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
聄 combines 耳 (ear) with 㐱, which likely contributes the sound. The exact historical development and original meaning are uncertain.
The left side is an ear 耳, and the right side 㐱 looks like a person with flowing hair. Picture an ear listening to a person's story, but the meaning remains unclear.
For シン, imagine a person 㐱 whispering a secret into an ear 耳: the shin (シン) of the whisper is the only sound the ear catches.