Getting strange repeated clicking sound on all recordings! How to help?

Hello. I am a voice actor who records in mono with 4800 sample rate and a bit depth of 24. Lately I am getting am incessant click-click-clicking on all recordings! A noise reduction takes care of most of it, but I can still hear it at the beginning and end of  pieces of vocals. I’ve tried rebooting my Macbook, rebooting Audition, unplugging and re-plugging all wires, and changing sample and bit rates. Nothing seems to work! I would ne greatly appreciative if someone could help he get rid of this problem. Thanks so much. I’m attaching a screenshot of the spectral Frequency Display so you can see a visual of the problem. 

EDIT: I’ve just discovered that the problem DOES NOT HAPPEN when I use my laptop’s built in microphone!! My audio converter is only about a year or so old, the mic is about 6 years old