Some schools of thought view various forms of metal as conductors for spiritual energies, while others can be viewed as tools for grounding (though, as metal is a strong conductor typically, the grounding possibility is somewhat more rare). As such, some people might consider piercings to have an influence on things like astral projection.
As for the tingling sensation, however, it could be from any number of possibilities. It could be a sort of awareness that comes with that heightened state of consciousness, that leaves you simply more aware of the piercings in your body on a physical level. It could be just a way that you react to the energies in question. It could just be you latching on to the physical sensation, and thus feeling a tingling of sorts as you become more grounded and come back from the efforts at projection.
So on, so forth.
I wouldn't worry overly. I've known many people who explore astral projection, and a solid majority of them have piercings of some variety. If you enjoy your piercings, I see no reason to remove them permanently.