I don't own a banjo, but I have a 3/4-sized acoustic guitar. Throw some paperclips on the strings and presto: Deliverance.
I wasn't sure how to approach this. When I hear about ghostly music, music that lingers longer after it was created, I start hearing Gavin Bryars' The Sinking of the Titanic. It was sort a reference point, both on what maybe to do, and what maybe to avoid.
How ghostly should this be? Do I go with a lot of reverb? Make it low volume? On the one hand I considered the different tropes used to indicate "ghostly" (or the like). "Let's not do that!", I thought. Too obvious. On the other hand, there are reasons certain things are used frequently. They're understood. They work.
I improvised a few things, recorded with my phone. I had meant to set up a proper mic, but slth kicked in. And the recording quality of the phone would (I expected) impart a more remote sound.
From my improve I extracted a number of loops, which I adjusted to fit a common tempo.
From there I played around in Renoise, bringing different loops in and out.
I wanted some other sound in there besides the ersatz banjo. I opted for ring-modulated sine tones. The idea was to try to offset the looping somewhat, add a bit more atmosphere.