The answer to 'why is my drain trap making gurgling noise' is that the drain trap is likely clogged or there is an issue with the plumbing vents. A gurgling drain trap is a common sign of a blockage or air flow problem in the plumbing system. This can cause water to be sucked out of the trap, allowing sewer gases to come back up through the drain.
Some common causes include a clogged drain, a blocked vent pipe, or a problem with the drain line. If the gurgling is accompanied by slow draining or a foul odor, it's likely a more serious issue that requires professional attention. In some cases, you may be able to clear a minor clog yourself, but if the problem persists, it's best to call a licensed plumber to diagnose and fix the issue.