For some people (including myself) when you record you can hear some static or background noise.
as you see the little bumps in the line are static (places where you aren’t talking but noise is being recorded)
To fix this you first highlight those sections of the audio file (just the part that has static)
After that you want to select the entire audio file (command a on a mac), or you can just highlight it if that is easier for you.
Go up to the effect button again and then click on noise removal again. Make sure you have the settings at the maximum settings (pictured below).