It works best with no playback in DT but it should work on Cycles too. So you trig tracks manually. Try also different layers of the same sound with subtle variations in other tracks; this gives depth and harmonics to your drone.
You can even work on playback mode and set a track sustain to inf and then trig a note manually by pressing the track button or a note in chromatic mode. Never tried this on DN but it should work.
Thanks for all the responses. I had a play with the m:c today. Set trig to ‘1st’, made sure the gate button was enabled, and set note length to inf…which produced the desired drone!