What is this?
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.
Common causes
- 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 to 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 an electrician 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
Typical cost
£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.
