The short answer
A steady low hum that is present regardless of volume, and changes when you unplug one device, is a ground loop. Fix it by plugging every connected device into the same mains socket or power strip, and where that is not possible, by isolating the signal path with a ground loop isolator rather than by removing an earth connection.
A ground loop happens when two connected devices are earthed at different points, creating a small voltage difference between them. Current flows through the signal cable’s shield to equalise it, and that current becomes an audible hum at the mains frequency, 50 or 60Hz depending on your country, usually with harmonics that make it a buzz rather than a pure tone.
Identifying what you have
- Steady low hum, constant regardless of volume: ground loop, or a mains-related fault.
- Hum that increases with volume: more likely a signal problem, a bad cable or a faulty source.
- Buzzing that changes when you touch the connector or cable: a poor connection or shield, sometimes a ground loop.
- Buzz that starts when a specific appliance runs: mains-borne interference from that appliance.
- High-pitched whine that follows screen activity or mouse movement: interference from a computer’s power supply or graphics card.
- Clicks and chirps on a phone-connected system: mobile radio interference, which is different again.
Finding the culprit
Disconnect everything from the amplifier or speakers
If the hum stops with nothing connected, it comes in through a signal cable. If it continues, the amplifier or the speakers themselves are the source.
Reconnect one device at a time
The hum will appear when you connect the offending device. That is your ground loop partner.
Try a different mains socket
Move the offending device to the same socket or power strip as the amplifier. This alone fixes a large proportion of cases.
Disconnect the TV aerial or cable feed
Aerial and cable connections are a very common ground loop path, because they are earthed at the point they enter the building. If the hum stops, you have found it.
Check with the device on battery if possible
A laptop running on battery has no mains earth. If the hum disappears on battery and returns when plugged in, it is definitively a ground loop.
Never solve a ground loop by defeating the earth pin on a mains plug, using an adapter that removes the earth, or cutting the earth wire. The earth is a safety connection and removing it can make a fault condition lethal. Every legitimate fix works on the signal path, not the mains earth.
The fixes, in order of preference
1. Single point of mains connection
Plug every interconnected device into the same socket or the same power strip. This minimises the voltage difference between them and is free. It is the correct first move in almost every domestic case.
2. Isolate the aerial or cable feed
If the loop comes through a television aerial or a cable connection, an aerial isolator or a coaxial ground loop isolator breaks the path while passing the signal. These are inexpensive and are the standard fix for hum in television and hi-fi systems.
3. Isolate the audio path
A ground loop isolator uses small transformers to pass the audio while breaking the electrical connection between the grounds. They are available for RCA, 3.5mm and XLR connections. Quality varies, and cheap ones can reduce bass slightly, and a decent one is inaudible.
4. Use an optical connection
Optical audio carries no electrical connection at all, so a ground loop through that path is physically impossible. If your equipment supports optical, switching to it eliminates the problem completely. This is why optical is often the recommended connection between a television and an audio system in a house with hum problems.
5. Use balanced connections
XLR and balanced connections reject induced noise by design. Relevant mainly for studio and higher-end equipment, and the correct answer where it is available.
When it is not a ground loop
- Cheap power supplies injecting noise. Swap a wall-wart adapter for a better one and test.
- Dimmer switches on the same circuit, which chop the mains waveform and put noise onto everything. Test with the dimmer fully on or off.
- A USB audio interface powered from a computer, where the computer’s own supply is the noise source. A powered hub or a USB isolator helps.
- Unbalanced cables running alongside mains cables, which pick up interference directly. Separate them and cross at right angles.
- A failing amplifier, where hum is present with all inputs disconnected. That is a repair rather than a configuration issue.
- Speaker cables too close to a power brick or a router, which is easy to test by moving things apart.
A quick diagnostic for computer-related buzzing: unplug the computer’s mains lead and run it on battery, or unplug its display cable. Screen-correlated noise almost always travels through the display connection or the shared power supply, and isolating either one identifies it in seconds.
What exactly is a ground loop?
Two connected devices earthed at different points, with a small voltage difference between them. Current flows through the signal cable’s shield to equalise, and that current is audible as hum.
Can I just remove the earth pin to stop the hum?
No. The earth is a safety connection and removing it creates a genuine electrocution risk. Use a signal-path isolator or an optical connection instead.
Why does the hum stop when I unplug the TV aerial?
Because the aerial is earthed where it enters the building, creating a second earth path. An aerial isolator breaks that path while passing the signal and is the standard fix.
Do ground loop isolators affect sound quality?
A good one is inaudible. Very cheap ones can roll off the bass slightly. Given that the alternative is a constant hum, the trade is usually worth it.
Why do I hear buzzing only when my computer screen is on?
Interference from the computer’s power supply or graphics card entering the audio path. Try a different socket, a USB isolator, or an optical connection to break the electrical path.
The order
Disconnect everything, then reconnect one device at a time to find which introduces the hum. Move all connected equipment to one mains socket. Isolate a television aerial or cable feed if that is the path. Use optical where it is available, since it makes the problem physically impossible. And never, under any circumstances, solve it by removing a mains earth.
