It is possibly that while you are using astral projection, you could be using the black knight (since you said ringing sounds) as well. Maybe it could possibly be what is giving the experience, but obviously my observation... not entirely. Maybe just as a booster or an enhancement for your experience. Plus, if you are 'projecting' yourself maybe the black knight is what your projecting into.?.? Also, I believe if you know that going in you could possibly get a better experience out of it.