Audacity’s “Normalize” effect has a “Remove DC offset” option which may be of help.
If you don’t want to change the volume don’t tick the “Normalize maximum volume to …”, just tick “Remove DC offset”.
You can get a little one there, but it tends to get hidden by the surrounding show. DC offset can give you a clear pop when there’s no show sound at all like when you’re trying to edit dialog word by word. It really stands out.
A common problem is to get half-way through editing and try to fix it then. Too late. You need to remove DC before you start editing.
This is drifting way off topic as the question from jahoh was answered accurately and succinctly in the very first reply (thanks Trebor).
DC offset is likely to produce a click when the track starts playing and when it stops playing. It can cause additional clicks if it is edited with audio that does not have DC off-set or has a different amount of DC offset. DC offset also reduces the amount of available headroom. In extreme cases it may cause unnecessary stress on amplifiers the playback equipment and can lead to premature failure of the equipment. DC offset is a 0Hz signal and should not be present in audio recordings. For more information see http://www.google.com/search?q=dc+offset