SvenArne
-The waveform shows square clipping

So it's in the audio waveform.
Were you aware of hitting the limit whilst recording?
Buffer adjustment will fix gapping, but not clipping.
 

Definitely way below 0 dBFS. The clicks are not amplitude related. Unless I misunderstood your reply?

Take a close look at the waveforms and describe the visual appearance of the clicks. That may provide a clue as to their source. Clocking issues will show up as narrow spikes, dropouts or sudden level changes. Overdriving the ADC may present itself as waveform peaks abruptly going to the opposite polarity. Both can sound the same. The latter is different than overdriving the interface's preamps, which won't result in clicks. The third possibility is buffer overruns due to too-small input buffers. That'll result in pretty obvious dropouts that last a millisecond or two. I guess a fourth (distant) possibility is a broken interface.
 

Its a long forgotten option ;) a few weeks ago, and you didn't say what Win ver. you are using but a win 10 update had many reinstalling audio drivers. Also if you're on a laptop you will need to Re Deactivate your onboard sound card.
*If you uninstall the onboard audio, reboot will reinstall them.
 
Peace!