What causes buzzing on my recordings?

What causes buzzing on my recordings?

On all my recordings there is some type of noise that cannot be identified. It sounds like a hissing or buzzing sound and I don't know if this is coming from my computer (such as a sound my own ears are not picking up but is being detected by the equipment) or if the actual microphone is making the noise. I just want it to stop as it's messing up my audio recordings.