Ticking or banging often occurs as the plastic vent pipe expands upward after being heated by hot water and water vapor flowing through the bottom toward the sewer. The warmed pipe then cools. The plastic pipe expands, but is held by friction at several points that pass through the wood framing. When the expansion pressure overcomes the friction of the surrounding wood or clamp, the pipe quickly moves until held by friction again. This can happen strongly enough to be a bang, or weakly enough to sound like ticking.