Hearing a knocking sound in your pipes when no water is running?
Yeah, that’s not just in your head. It’s one of those strange, annoying things that can make you stop in your tracks and wonder what’s going on behind the walls.
The good news is, it’s usually not a plumbing emergency. But it is something you’ll want to figure out before it turns into a real problem.
In this post, we’ll shed some light on knocking pipes when water is not running and how to fix it.
Why Do I Hear Knocking Pipes When Water Is Not Running?
There are a few sneaky reasons pipes make knocking sounds when water is not running. Here are the most common causes:
#1. Thermal Expansion
This is a quiet culprit that gets a lot of people.
When water heats up like after someone takes a hot shower or your water heater kicks on, the metal pipes expand. Then, as things cool down, they contract.
If the pipes are sitting tightly against wood, metal, or even concrete, they can make clicking, popping, or knocking sounds as they shift around.
It’s harmless in most cases, but the sound can echo through walls like something more serious.
This is super common in pipes that were never insulated properly or installed with enough space to move.
Also Read: Water Heater Sounds Like Water Running
#2. Water Hammer
Water hammer happens when flowing water is suddenly stopped like when you shut off a faucet or your washing machine valve closes quickly. That fast stop creates a pressure shock that bangs around in the pipes.
Normally, this happens right after water is turned off.
But sometimes, if your plumbing system isn’t balanced or doesn’t have proper air cushions or arrestors, the trapped pressure can bounce around even without active water flow.
That could cause knocking sounds randomly during the day or night, even when nothing’s running.
#3. Loose Pipes
If your pipes aren’t clamped down properly behind your walls or in your basement, they’ll move around when water flows through them or even when there’s a change in pressure or temperature.
That movement causes the pipe to knock against the framing, subfloor, or nearby pipes.
This can sound like a light tapping or a full-on thud, depending on the size of the pipe and what it’s hitting. The more unsecured the pipe is, the more dramatic the knocking can sound.
If your house is older, or the plumbing wasn’t installed perfectly, this could easily be your culprit.
#4. Air In The Pipes
Another reason behind knocking pipes when water is not running is air in the system.
Air pockets can develop in your plumbing system for a few different reasons – maybe the water main was shut off recently, or work was done on the system.
When air gets trapped and then moves through the pipes, it can make strange noises, including knocking or bubbling sounds.
Sometimes, it’ll sound like someone’s lightly tapping inside your walls. Other times, it’s louder and more aggressive. Either way, it’s one of those problems that’s easy to fix with a little draining (more on that in a sec).
Also Read: Do I Need a Plumber for Low Water Pressure?
#5. Well Pump Or Pressure Tank Cycling
If you have a well system, this is a big one to check.
When the pressure tank or pump starts cycling too frequently (or at the wrong times) it can create a knocking or banging sound. Even when you’re not using any water.
That cycling means the pressure in the system is fluctuating more than it should. This can lead to sudden shifts in the water pipes and those can knock.
Sometimes it’s just wear and tear. Sometimes it’s a sign the tank’s bladder is going bad.
#6. Neighboring Units Or Shared Pipes
Live in an apartment or a townhome? You might be hearing your neighbor’s plumbing!
Pipes often run through shared walls or ceilings, and the sounds don’t always stay on their side.
So if their washer kicks on, or their toilet runs a bit too long, it could trigger some knocking that you hear, especially late at night when everything else is quiet.
How To Fix Knocking Pipe Sounds
Getting to the bottom of knocking pipes doesn’t always mean tearing open walls. A few simple checks can go a long way. Here’s how to troubleshoot the issue step by step:
Check For Leaks
Even the smallest leak can mess with your system’s pressure.
Do a full walkthrough of your home. Check under sinks, around toilet bases, and near hose bibs. Look for any signs of dripping or running water.
Also, listen – sometimes you’ll hear a faint hiss or trickle before you see it.
Want a quick way to check? Turn off all your water-using fixtures and appliances, then watch your water meter. If it’s still spinning, something’s leaking.
Also Read: Shower Valve Sticks Out Too Far
Drain The System
This is a good trick if you suspect air in the pipes.
Turn off the main water valve to your house. Then open all your faucets (hot and cold) from top to bottom – yes, even the outdoor hose bibs. Let everything drain completely.
Once that’s done, turn the water back on slowly and let the air escape.
This can help reset the system and eliminate any air pockets that might be making noise.
Secure Loose Pipes
If you suspect the pipes are shaking around, you should go secure them.
Head to your basement or crawlspace and look for any visible pipes. If they wiggle when touched, they need to be strapped down. You can use pipe clamps or padded brackets to keep them from banging against joists or walls.
Be careful not to overtighten though – give them room to expand a little, especially the hot water lines.
Inspect Water Pressure
Too much pressure = trouble. You want it to sit somewhere around 40–60 psi.
If it’s much higher than that, it can stress your pipes and cause knocking. You can pick up a cheap water pressure gauge at any hardware store and test it yourself.
If it’s too high, installing a pressure-reducing valve can make a huge difference.
Install Or Recharge Water Hammer Arrestors
If you’ve got an older home, you might not have water hammer arrestors.
These are little shock absorbers that go near fixtures and appliances to cushion sudden pressure shifts.
If you already have them and they’re not helping, they might need to be recharged. Some styles just need to be drained and refilled with air. Others might need to be replaced entirely.
Not super handy? This is one job where a quick visit from a plumber could be worth it.
When To Call A Plumber
You’ve poked around, tried a few things, and the knocking’s still happening?
Here’s when it’s smart to get a pro involved:
- The knocking is getting louder or more frequent.
- You see signs of leaks, damp spots, or water stains.
- The noise happens in a spot you can’t access.
- You’re on a well and think your tank or pump might be involved.
- You’re not comfortable making adjustments to water pressure or arrestors.
A licensed plumber can trace the source quickly, especially if it’s hidden behind walls or ceilings. Plus, they’ll have the tools to diagnose and fix it without guesswork.
Bottom Line
Knocking pipes are annoying, no doubt. But they’re not usually a big emergency.
Most of the time, it’s something like loose pipes, air in the lines, or pressure that’s just a bit off. Fixing those can be pretty simple with a little time and a few tools.
If you’ve tried everything and the knocking still won’t quit, or it’s getting worse, go ahead and call in a pro.
You don’t want to ignore it and end up with bigger repairs later!