Electrical Humming Noise At Night

You can hear an electrical humming or droning noise at night that is not there during the day.

What's happening?

An electrical humming noise that is more noticeable at night is a common complaint. The sound has often been present all along but is masked by daytime background noise. At night, when the house is quiet, the mains frequency hum (50Hz in the UK) or vibrations from electrical equipment become audible. However, a new or increasing hum can indicate a developing fault.

What usually causes it?

Transformer hum from a doorbell transformer, charger, or low-voltage lighting
Smart meter or electricity meter vibrating
Consumer unit or individual MCBs humming under load
Fridge, freezer, or boiler operating on a timer and cycling on at night
Mains hum transmitted through the building structure from outside supply cables
Economy 7 or storage heaters switching on during off-peak hours

Is it dangerous?

Usually not dangerous if the hum is steady and has been present for a long time. However, a new hum or one that is getting louder could indicate a loose connection, a failing component, or an overloaded circuit. If the hum is accompanied by warmth, a burning smell, or flickering lights, it should be investigated promptly.

Can I fix it myself?

Try to locate the source by listening carefully around the house at night. Common sources include doorbell transformers (usually near the consumer unit), phone chargers, broadband routers, and other small transformers. Unplug suspect devices one at a time to see if the hum stops. If the sound comes from the consumer unit or a socket, call an electrician.

When should you call an electrician?

Call an electrician if you cannot identify the source, if the hum comes from the consumer unit or a socket, if it is a new sound that has appeared suddenly, or if it is accompanied by any other electrical symptoms like flickering lights, warmth, or burning smell.

What will the electrician actually do?

Systematically isolate circuits to identify the source of the hum
Inspect the consumer unit for loose connections or vibrating components
Check for faulty transformers (doorbell, lighting, etc.)
Test the mains supply for abnormalities that could cause excessive hum
Replace any identified faulty or noisy components

What will it cost to fix?

£80–£200

The main cost is the electrician's time to diagnose the source. Once identified, the repair is usually straightforward — replacing a transformer, tightening connections, or similar.

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Frequently asked questions

We’re happy to answer all your questions.

Why can I only hear it at night?

In most cases the sound is present all the time but is masked by daytime noise — traffic, appliances, conversation. At night, with everything quiet, the hum becomes noticeable. Occasionally it genuinely only occurs at night due to off-peak equipment switching on.

Could it be coming from outside my house?

Yes. Street-level transformers (the green boxes on pavements), substations, or even a neighbour's equipment can transmit hum through the ground or building structure. If you suspect an external source, contact your DNO.

Is electrical hum always 50Hz?

The fundamental UK mains frequency is 50Hz, but the audible hum is often at 100Hz (the second harmonic) because the magnetic field oscillates twice per cycle. This is the classic 'mains hum' tone.

Can a smart meter cause humming?

Some smart meters do produce a faint hum, especially older models. If you suspect your smart meter, contact your energy supplier — they can arrange an inspection or replacement.

Sources & References

Mains Hum In The HouseLow risk Fuse Box Buzzing Or HummingHigh risk Light Fitting BuzzingLow risk Electrical Fault Finding Cost£80–£250 Fuse Box Replacement Cost£350–£800

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