How long have you had it? Is this unusual behaviour for it or has it always done it? Most plecos aren't really great aquarium fish from the perspective that you never see them. I know a guy who only has plecos and he had the fish club around to see his fish and they all complained about seeing a bunch of empty tanks. I cleaned a tank out and removed a bunch of items from the tank the other day and I was shocked at the size of one of my L066. All I ever see of them is a bit of tail poking out of their cave.