My colleague confirmed this impression; seems to require closed headphones. My theory is that we "hear" a spectrally complementary function, for example notches when there where strong partials, similar to how we see negative afterimages when we look at a static image for a while and then move the eyes to something else.
There is a reference from German psycho-acoustician Zwicker about an "acoustical aftertone", describes as sine components after prolonged hearing of a notched noise.
@sciss yes! I know exactly what you are talking about. I thought I was the only one, and was too scared to talk about it.
Auditory afterimage (neurological explanation): https://www.brainnrg.org/files/publicationmodule/@random45f5724eba2f8/pid1799.pdf
Also about the metallic effects: https://asa.scitation.org/doi/full/10.1121/1.2828057
@mathr @sciss Absolutely! A friend of mine does this something similar with things called "auditory distortion products", which can weird inner-ear modulations to happen. His compositions can be really trippy to listen to. A while ago he made some software for it: http://alexchechile.com/projects.html