A sink that gurgles despite draining at a normal speed is usually experiencing pressure imbalances caused by an obstructed roof vent stack or a shared branch line restriction. When a washing machine, toilet, or bathtub discharges water elsewhere in the house, it pushes air through the drainage system. If the roof vent is blocked by leaves, air cannot escape upward and is forced to bubble up through your sink P-trap, creating gurgling noises without a surface clog. Verification: Inspect your roof vent stack to ensure proper exterior airflow.
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