Sounds like a job for De-Esser , (Audacity specific De-Esser plugin here).
http://manual.audacityteam.org/man/effect_menu.html#nyquist_effects
If you’re using Audacity on Windows there are free VST De-esser plugins, e.g. SpitFish , TDR Nova.
NB: Only download 32-bit versions VST plugins for Audacity, even if your computer OS is 64-bit.