If its brick wall don't worry to much about covering them, no sound produced by any machine is likely to to penetrate it with much energy left unless the sound source is applied directly to the wall e.g. drilling into the wall with a hammer drill. If you are on a budget then something like old carpet + underfelt inside the ceiling between the trusses will makes a good difference. The basic idea is to get things as air tight as possible and damping where you cannot make it air tight. Think along the lines of how well modern cars are sound proofed.