Audacity

Basic Effects: Removing Background Noise

When recording audio, there are parts on most tracks where there is no intentional audio being recorded. These parts are meant to be silent. However, many times the input device will pick up small levels of audio from the immediate recording environment. This is considered background noise and can be very noticeable during playback. Using the Noise Removal effect, you can define and eliminate background noise on your track.

Using the Selection toolselect an area of the track that contains only background noise
From the Effect menu, select Noise Removal...
The Noise Removal dialog box appears.
Under Step 1, Click GET NOISE PROFILE
Audacity determines what data in the audio file qualifies as noise, and the dialog box closes.
Select a part of the audio track that you want to remove noise from
From the Effect menu, select Noise Removal...
The Noise Removal dialog box appears.
Under Step 2, adjust how much noise you want filtered by using the Less/More slider
Click PREVIEW
Repeat steps 6 and 7 until you have the desired result
When satisfied click REMOVE NOISE
The background noise is removed.