Remove the porcelain tank lid carefully. Set it on a towel (never on a hard floor—it will crack). Look for:

Ignoring a noisy toilet is like ignoring a "Check Engine" light—it might be fine today, but it’s definitely costing you money in wasted water.

One of the most unsettling sounds to echo from a supposedly empty restroom is the automatic flush. In the dead of night or during a quiet afternoon lull, the sudden WHOOSH of water can sound like a ghostly intruder. Usually, the culprit is a hyper-sensitive sensor on an automatic urinal. A stray fly, a shifting shadow, or a sudden change in light can trick the infrared eye into thinking a user has stepped away. The result? A restroom that flushes for no one.

This is perhaps the loudest and most startling noise. It usually happens right as the tank finishes filling. It’s caused by a loose washer or a failing part in the ballcock assembly vibrating against the water flow.