Hi, last week we smelled gas and a Southern Gas Network (SGN) engineer came and removed the old fitting attachment on an old pipe in our living room (which he thought looked like an old bayonet fitting for an oven although strange that was in our front room) and capped off the pipe. He tested for pressure etc and confirmed it was all safe. However just now it sounded like the pipes were rattling in the walls. Is it possible for a pipe that's capped off to have pressure build up inside it? I know I sound paranoid but with no idea how these things work I'm worried that we are moments away from an explosion or something. Any advice is greatly appreciated. Thank you!