Quick audio cleanup filters in Kdenlive
Currently your best bet is to extract the audio of the clip before you start editing, and then importing it into Audacity, which has a great toolbox for dealing with outside noise.
Once done, you can export from Audacity and back into Kdenlive.
It's a workaround, and very labor intensive. It would have been much nicer to be able to apply some basic audio filters directly in Kdenlive.