Spooky Plumbing Noises Explained: Gurgling Drains, Water Hammer and the Toilet That Runs by Itself

Halloween’s a fine night for strange noises, just not from your plumbing. Most of the bumps, gurgles and hisses in a house have a boring explanation, and a few are early warnings worth acting on. Here’s what each sound usually means, what you can check yourself, and which ones mean you should pick up the phone.

Why is my toilet running by itself?

Nobody has touched the toilet, but every so often it refills for a few seconds. That’s a phantom flush: water slowly leaking from the tank into the bowl, usually past a worn or warped flapper. When the tank level drops far enough, the fill valve opens and tops it off.

The dye test

1. Take the lid off the tank and add 5 to 10 drops of food coloring to the tank water.
2. Don’t flush. Wait 15 to 30 minutes.
3. Look in the bowl. Any color means the flapper, or the seat it seals against, is leaking.

If the bowl stays clear, look at the overflow tube in the middle of the tank. If water is trickling into it, the fill valve is set too high or isn’t shutting off. Lower the float so the water stops at the fill line marked inside the tank, usually about an inch below the top of the tube.

A flapper is a cheap part and about a ten-minute job: shut off the supply valve behind the toilet, flush to empty the tank, unhook the old flapper and clip on the new one. If the flush valve seat is pitted or the tank bolts are corroded, that’s a bigger job; toilet repair runs $125–$275.

Pro tip: Take the old flapper with you to the hardware store. Most toilets use either a 2-inch or 3-inch flush valve, and the wrong size will leak right out of the package.

Why do my drains gurgle?

Gurgling is air being dragged through water. Your drain is gasping. The two common causes:

• A venting problem. Every drain needs air from the vent pipe on the roof to flow smoothly. If the vent is plugged with leaves or a nest, or frosted shut during a sub-zero Iowa cold snap, draining water pulls air through the nearest trap instead, with a glug. Some sinks have an air admittance valve under the cabinet instead of a roof vent, and those can stick shut.
• A partial clog. Water squeezing past a blockage pulls air with it. If one sink gurgles, it’s usually that branch line. If the toilet glugs when the washer drains, or the tub burps when you flush, the clog is farther down, often in the main line.

Gurgling that comes with a sewer smell often means a trap is being pulled dry; our post on sewer smell in the basement walks through that. If several drains gurgle and run slow, it’s time for drain cleaning before it turns into a backup.

What’s that banging when the water shuts off?

That’s water hammer. Moving water has momentum, and when a valve slams shut, the water stops all at once. The shock wave rattles the pipe against whatever it’s next to. The usual triggers are washing machines and dishwashers, whose valves snap shut in a split second, along with ice makers and single-handle faucets closed fast.

Fixes, roughly cheapest first:

• Close faucets gently. Free, and it helps.
• Strap loose pipes. Pipes hanging loose in a basement ceiling or crawlspace bang louder. Extra straps quiet them.
• Add water hammer arrestors at the washer and dishwasher. They’re small cylinders with an air cushion that soaks up the shock. Older homes often had plain air chambers that filled with water years ago and quit working.
• Check your water pressure. A hose-thread pressure gauge from the hardware store tells you in a minute. Most homes do well somewhere around 50 to 70 psi. If you’re seeing much above 80, high pressure is making the hammer worse. If your home has a pressure-reducing valve and it’s failing, replacement runs $350–$700.

Pro tip: Screw the gauge onto an outdoor faucet before you winterize it this fall, and check it once in the evening too. Pressure can run higher when the neighborhood isn’t using much water.

Why are my pipes whistling or squealing?

A whistle is water forced through a small opening: a worn faucet washer or cartridge, a toilet fill valve squealing as it refills, a shutoff valve left partly closed, or a failing pressure-reducing valve. If it happens at one fixture, it’s a part in that fixture. If it happens everywhere, look at pressure or the main valve.

Why is my water heater popping or rumbling?

Popping, crackling or rumbling from a gas tank water heater is almost always sediment. Central Iowa water is hard, and the minerals settle on the bottom of the tank. Water gets trapped under that crust, the burner boils it, and you hear it pop. Electric tanks can sizzle for the same reason as the elements get coated.

Sediment isn’t dangerous by itself, but it wastes energy and wears out the tank bottom. A flush helps if it’s done regularly. On a tank that’s 10 years old and has never been flushed, flushing may not break up the hardened layer, and if that tank is also leaking, it’s time to plan for a new one; our water heater cost guide has the numbers.

A different sound, a hiss from the relief valve on the side or top of the tank or water dripping from its discharge pipe, isn’t sediment. That valve opens when pressure or temperature gets too high. Call us about that the same day.

And the ticking or creaking you hear in the walls after a hot shower? Pipes expand as hot water runs through them and rub against joists and straps. That one’s harmless.

I hear dripping inside the wall. What now?

Act today. A drip or hiss inside a wall, floor or ceiling when nothing is running is a supply leak until proven otherwise, and supply lines are under pressure around the clock.

Quick check: turn off every faucet and water-using appliance, then look at your water meter. Most meters have a small leak indicator that spins when any water is flowing. If it’s moving with everything off, you have a leak somewhere. If water is showing on a ceiling or wall, shut off the main and call us at (515) 494-5483. Our leak repair service uses electronic leak detection to pinpoint the spot, so the opening in your wall stays small.

Which plumbing noises are harmless and which mean call?

Noise	Likely cause	How urgent	Typical fix
Toilet refills by itself	Leaking flapper or fill valve	This week	DIY flapper, or toilet repair $125–$275
One drain gurgles	Partial clog in that branch	Soon	Drain clear $95–$200
Several drains gurgle and run slow	Main line clog or vent problem	Soon, before it backs up	Main line clearing $200–$350
Bang when a valve closes	Water hammer, loose pipes or high pressure	Soon	Straps and arrestors; PRV replacement $350–$700
Whistle at one fixture	Worn washer, cartridge or fill valve	When convenient	Toilet repair $125–$275 or faucet install $200–$450
Popping water heater	Sediment	Plan a flush	Water heater flush $100–$200
Hissing at the relief valve	Pressure or temperature problem	Same day	Valve replacement $150–$350, plus a look at why
Drip or hiss inside a wall	Hidden supply leak	Now	Leak detection $150–$400; accessible repair $200–$500
Ticking pipes as hot water runs	Thermal expansion	Harmless	Nothing needed

Planning ranges for the Des Moines metro in 2026; your written quote depends on the equipment, access and what we find on site.

What can I handle myself, and when should I call?

Fine to do yourself: flappers, fill valve height, strapping loose pipes you can reach, a pressure test with a gauge, and plunging a single slow drain.

Pro tip: Before you flush an older water heater yourself, crack the drain valve open and closed once. Old plastic valves sometimes won’t reseal. If it drips after closing, stop and call; a drain valve swap is a small job on a dry day and a mess on a flooded one.

Call for anything dripping inside a wall, a hissing relief valve, repeated gurgling with slow drains, pressure readings well over 80, or a water heater that’s popping and leaking. We answer 24/7 at (515) 494-5483, and you’ll get a written quote before any work starts. Here’s hoping the only thing knocking tonight is a trick-or-treater.