Maybe the source was compressed audio instead of flac/wav?
Edit: the source is an mp3, which removes audio frequencies based on perception/masking with other frequencies. It's perfectly normal that it is showing artifacts. A better source is needed.
Edit: the source is an mp3, which removes audio frequencies based on perception/masking with other frequencies. It's perfectly normal that it is showing artifacts. A better source is needed.
Edit: I uploaded the original FLAC to my web server last night, before I decided that MP3 would be more convenient:
https://mwcampbell.us/tmp/spleeter-demo/jonathan-coulton-re-...