It is too loud

Normal noises

• A continuous fan. Broadband and steady. Most people habituate to it within a night or two - it is effectively white noise.
• The compressor starting and stopping. A distinct change in note and level as the humidistat cycles. This is the sound people actually complain about, because human attention locks onto change rather than level.
• Water trickling into the bucket. Intermittent, and the machine working.
• A brief gurgle or hiss after the compressor stops. Refrigerant equalizing. Normal on any refrigeration appliance.
• A pump running for a few seconds at intervals. On a pump model, that is the reservoir emptying.

Noises that are not normal

1. 1A rattle. Usually something loose - a panel, a filter not seated, a fan guard, or an object on top of the machine. Check the easy things before assuming anything internal.
2. 2A grinding or scraping sound that tracks the fan. The fan blade contacting something, or a failing fan bearing. This will get worse.
3. 3A loud buzz or hum that starts and stops with the compressor. A compressor mount or a starting-component fault. Worth a warranty call.
4. 4A new noise that was not there. Whatever it is, a change is the signal. A dehumidifier that has run the same way for two seasons and then sounds different has changed for a reason.
5. 5A pump running constantly rather than in short bursts. That usually means the route is beyond its reach, and running continuously will burn it out. Pump lift and distance.

Four things that genuinely reduce the noise you hear

1. 1Put it on a mat. A compressor unit on tile or concrete puts its vibration straight into the structure, and the floor becomes a soundboard. A rubber mat costs a few dollars and is the highest-return change available.
2. 2Size it correctly. An oversized unit reaches its target quickly and shuts off, then restarts twenty minutes later - more cycling events, which is more of the sound people notice. A correctly sized machine runs longer, steadier cycles. This is the opposite of the usual buying advice and it is right.
3. 3Move it away from walls and corners. Hard surfaces close to the intake and exhaust reflect and amplify. It also helps airflow, which the machine wants anyway.
4. 4Run it at a lower fan speed if the unit allows it. The compressor dominates the total, so this is a modest change - but it is free and it does something.

When the answer is a different machine

If the room is one you sleep in and the compressor cycling is intolerable, no adjustment will fix it - the machine contains a compressor and it will cycle. The options are a smaller compressor unit correctly sized to the room, or a machine with no compressor at all.

Thermoelectric units are effectively silent because there is no compressor to cycle. The cost is capacity: about one pint a day against a 30-pint machine's thirty. That is the right trade for a wardrobe and the wrong one for a room with a real humidity problem. Quiet dehumidifiers.