There is a free DeClicker plugin for Audacity which will automatically remove clicks, here.
Now the bad news, that plugin is slow: at the settings required, (shown above), processing-time is about double the playback-time , (on my computer, YMMV). Also that plugin may choke on audio which is hours long, you’ll have to apply it in installments, (Try 15 minute chunks, then see if you can get away with longer sections).
The code below if put into Nyquist prompt removes the mains-hum, (no effect on clicks)
(setf *track* (notch2 *track* 43 5))
(setf *track* (notch2 *track* 60 10))
(setf *track* (notch2 *track* 90 10))
(setf *track* (notch2 *track* 212 10))
(highpass8 *track* 20)
