Ask HN: Is taking input from your microphone a TRNG?

Working on a project where the goal is to generate a secure key from my device. Ive used dev/urandom in the past but it's always felt like a black box and I have no way to prove it's completely random.

Then it dawned on me while I was playing guitar...why don't I make a program that records audio and hashes the input. Is this not a TRNG? The input would never repeat since there will always be slight difference.

What am I missing?