I'm installing a closetmaid shelf in my closet in a 2nd floor bedroom. I was drilling behind drywall and on one of the holes I marked I hit some kind of plastic. I'm not sure if its a wall or pipe, but it is white in color (I've already shaved off pieces of it with the drill). I'm confused because I used a high quality stud finder and it shows nothing there. Well, the plastic is technically 1/2 inch behind the drywall so the stud finder possibly missed it (maybe).
This hole I drilled into is close to the edge of another wall (a wall of one side of the house). The plastic is adjacent to another stud, though. Doubtful that it might be plumbing (subjective) since the side of this wall is not shared by any walls of a bathroom. The wall is directly below an attic and the floor below are just regular living rooms.
Any idea what I drilled into? and whatever that may be, would it be safe to drill into ?