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Noise Between Walls
Noise between walls usually means one of two things. Either something inside the wall is making a sound (a knocking pipe, a ticking duct, a mouse), or sound from the next room or the neighbors is coming through the wall. The causes and the fixes are completely different, so the first job is working out which one you have.
Quick answer If the noise starts in the wall itself, it is usually pipes (knocking or banging), ducts or pipes expanding as they heat and cool (ticking), wiring (buzzing), or pests (scratching). If you are hearing voices, TV or footsteps from next door, the wall is too light or leaky: seal the gaps and outlets, then add mass with mass loaded vinyl and drywall.
Noise in the Wall or Through the Wall?
- It’s in the wall if the sound is mechanical (knock, tick, buzz, scratch, drip), happens when nobody is next door, or lines up with the heat, the AC, a tap or a toilet running.
- It’s through the wall if you can make out voices, music, a TV or footsteps, and it follows your neighbors’ routine.
Put your ear against the wall in a few places. A noise inside the wall is loudest at one spot. Sound coming through the wall is spread across it, and often loudest at outlets, along the floor or near the ceiling.
What’s Making Noise in Your Walls?
| What you hear | Likely cause | What to do |
|---|---|---|
| Bang or knock when a tap or appliance shuts off | Water hammer: water stopping suddenly in the pipe | A plumber can fit water hammer arrestors or secure loose pipes |
| Ticking, popping or cracking as the heat or AC runs | Ducts, pipes or framing expanding and contracting | Usually harmless; loose ducts or pipes can be strapped or padded |
| Buzzing or humming | Wiring, a loose connection or an overloaded circuit | Call an electrician (see below) |
| Scratching, scurrying or chewing, often at night | Mice, rats, squirrels or insects | Pest control, and seal the entry points |
| Dripping or running water when nothing is on | A leaking pipe | Shut off the water and call a plumber |
| Creaking, mostly at night | The house cooling and settling | Normal, unless cracks are growing |
Don’t ignore a buzzing wall Buzzing or humming from an outlet, switch or wall, especially with a warm cover plate, a burning smell or flickering lights, can mean a dangerous electrical fault. Turn off that circuit at the breaker and call a licensed electrician.
None of these are soundproofing problems. Insulation and mass in the wall can make a ticking duct or a knocking pipe quieter, but the fix is at the source.
Why Can I Hear Everything Through My Walls?
Most interior walls, and many apartment and townhouse walls, are a single row of studs with one layer of drywall on each side. That is light, hollow and stiff, so it vibrates easily and passes sound straight through. The usual reasons it’s worse than it should be:
- Not enough mass. Light walls block less sound. A plain stud wall rates about STC 33 to 39; apartment walls are supposed to reach at least STC 50.
- An empty cavity. With no insulation, the hollow space between the drywall resonates like a drum.
- Gaps and outlets. Sound pours through cracks at the floor and ceiling and through electrical boxes, especially outlets placed back to back on both sides of the wall.
- Flanking paths. Sound goes around the wall: over it through a shared ceiling space or attic, through ducts and vents, under doors, or along a shared floor.
How Sound Travels Through Walls
Sound reaches you through a wall in two ways. Airborne sound, like voices and TV, pushes on the wall, makes it flex, and the far side radiates the sound into your room. Impact sound, like footsteps, slammed doors or a washing machine on the floor, puts vibration straight into the building’s structure, which carries it into your walls. Low bass from music and subwoofers is the hardest of all, because it moves heavy structures easily.
How to Stop Noise Through Walls
- Seal the gaps. Run acoustical caulk along the baseboards, the ceiling line and around pipes, and seal around electrical boxes on the shared wall. Add a door sweep and seals to the door. This is cheap and often the biggest single improvement.
- Fill the cavity. If the wall is open or being redone, put mineral wool or fiberglass insulation in the stud space.
- Add mass. A layer of Wall Blokker™ mass loaded vinyl under drywall adds roughly 6 to 12 STC points. On a finished wall it goes over the old drywall, under a new layer: see MLV on an existing wall. To choose the right one, see the best mass loaded vinyl.
- Decouple. For bass and footsteps, hang the new drywall on resilient channel or sound isolation clips so the wall can’t pass vibration straight through.
- Close the flanking paths. Line or reroute shared ducts, and block the ceiling space above the wall if it’s open to the next unit.
For the full step-by-step on a finished wall, see how to soundproof existing walls. If the noise is your neighbors, start with how to block noise from neighbors.
Frequently Asked Questions
Why do I hear noises inside my walls at night?
Usually the house cooling down: ducts, pipes and framing contract and tick or creak as the temperature drops. Scratching or scurrying at night is more likely mice or other pests, which are most active after dark.
Why can I hear everything through my walls?
Most walls are a single row of studs with one layer of drywall each side, often with no insulation. They are light and hollow, so they pass sound easily, and gaps and back-to-back outlets make it worse.
What causes knocking in the walls?
A bang when a tap, dishwasher or washing machine shuts off is usually water hammer in the pipes. A plumber can fit water hammer arrestors or secure the loose pipe.
Is a buzzing noise in the wall dangerous?
It can be. Buzzing from an outlet, switch or wall can mean a loose or overloaded electrical connection. Turn off that circuit at the breaker and have an electrician check it, especially if you notice heat or a burning smell.
How do I stop noise coming through a shared wall?
Seal the gaps and outlets with acoustical caulk first, then add mass: mass loaded vinyl under a new layer of drywall. For bass and footsteps, hang that drywall on resilient channel or isolation clips.
