The answer to 'bathtub making gurgling noise' is that a gurgling sound in the bathtub is usually caused by a blocked or partially blocked drain line. This can be due to a buildup of hair, soap scum, or other debris in the drain, which restricts the flow of water and causes air to be drawn back into the tub, creating the gurgling sound.
Other common causes include a blocked vent pipe, a problem with the drain trap, or issues with the plumbing system further down the line. Gurgling noises can also be a sign of a more serious problem, such as a sewer line blockage or a problem with the septic system.