I've just found tons of greyed out media monkey libraries in my Printers and devices section. What are they and how can I stop it happening?

Hi, I've been using MM since V3 and it's been great but I've now got a strange problem: I'm playing ripped FLAC files mostly from my PC via USB in to a standalone DAC. Theres a strange tizzy distortion appeared. At first I thought it was crap recording so I listened to it on Qobuz and it's great ...