The De-Clicker and De-Esser plug-ins are popular with some audiobook authors. The purpose of the De-Clicker is to remove mouth clicks and similar clicky sounds from the recording, while De-Esser is for reducing excessive sibilance (hissy “s” and “shh” sounds).
These plug-ins have horrible code and are only available on the understanding that there is no technical support and no documentation.
Here they are:
The Audacity community forum has some additional information about these plug-ins, including usage tips. The Audacity forum topic is HERE.