Full disclosure: I know very little about electrical work and was hoping for an easy fix.
I have been getting a buzzing from my dimmer every time the dim feature is used, and I read that a low quality dimmer can cause this. I read that this one is good, so I purchased it as a replacement: https://www.amazon.com/gp/product/B000BOA23U
I flipped the breaker and then tested the light switch to make sure the light wouldn't turn off. I removed the old dimmer, which had two black wires and a green wire.
Both black wires were connected to their own black wires in the wall (seen below coming toward the camera), but the green wire was not connected to anything at all. I'm really not sure what to do as I suspect that not having a ground on a dimmer could be causing the buzzing and could be unsafe. Here's what it looks like in the wall:
So...what should I do to make this safe?