Clean recorded audio with Audacity

When you've finished recording:
- Ctrl A to select all, Effect - Normalize (this'll adjust the waveform so that it's
a consistent volume)

- Select ONLY the beginning, before you begin speaking:
Effect - Noise Reduction - Get Noise Profile - OK

Ctrl A to select all again
Effect - Noise Reduction - OK.

Normalize it again until your audio sounds clear.
Repeat if necessary.