The answer to 'supply line making gurgling noise' is that a gurgling sound in the water supply line is usually caused by a blockage or air in the line. This can be due to a clogged pipe, a problem with the water pressure, or a leak in the line.
Some common causes include a clogged aerator on the faucet, a buildup of mineral deposits, or a problem with the main water line. The gurgling noise may be accompanied by low water pressure or water that comes out in spurts. In some cases, the gurgling can be caused by air getting trapped in the line, which can happen if there's a leak or if the water supply is turned off and then turned back on.