A sink that gurgles despite draining normally is usually experiencing pressure imbalances caused by an obstructed roof vent stack or a shared branch line restriction. When a washing machine or toilet 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 distinct gurgling sounds without a surface clog. Verification: Inspect your roof vent stack to ensure proper exterior airflow.
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