The noise that is sometimes heard in a B vent pipe can be attributed to the movement of system parts against each other or against the structure. It can also be caused by changes or additions to the system. Loose roof flashing attached to the pipe can cause noise as well. The normal expansion and contractions of metal that occur with variations in temperature can also lead to popping sounds or other similar noises being heard. Some manufactures discourage the use of sheet metal screws in the installation of a B vent pipe, and assert that the use of such screws use can lead to excessive noise in the vent pipe.