[mclingo]

I decided to try a new, clean install of Kodi 18.4 with MPC-HC as an external player, and, to my surprise, the noise was still there. So, I closed Kodi, tried MPC-HC on its own, and guess what? No noise.

So, I have to conclude that Kodi is interfering with the signal somehow. I turned off GUI sounds, keep audio device alive, send low volume signal, all off. I even changed the audio device to something else. Still the noise persists.

Now I'm in a quandary. Any suggestions?

if its not KODI DS then  i'd log it on the main forum, you'll get greater coverage there, KODI DS is a much smaller subset of KODI users.