The answer to 'why is my bathtub making gurgling noise' is that the gurgling is usually caused by a blockage or obstruction in the drain pipe. This creates a vacuum in the pipe that allows air to be sucked back up through the drain, making a gurgling sound. Common causes include hair, soap scum, or other debris building up in the drain over time.
The gurgling noise may also be accompanied by slow draining water, foul odors, or even water backing up into the tub. If the issue is not addressed, it can lead to more serious problems like a completely clogged drain or even sewer gas seeping into your bathroom.