Every night in my apartment in Nice, I heard the sound of marbles rolling across the floor upstairs. Or perhaps they were pins being hurled to the floor. Or maybe the building—my apartment, where Matisse once lived, dated from 1830—was haunted by the ghost of a child who loved playing marbles.
But I soon learned that the rolling-marble sounds weren’t unique to my apartment.
Alyssa Schwartz lives in an apartment in Toronto, built in 2001. “I don’t think it’s just in France,” she said. “I live in a condo in Canada and have this, and last week, when I was in Florida, someone was complaining to me that their upstairs neighbor is always rolling marbles. I feel like it’s a really common building sound.”
Eileen Smith, who used to live in an apartment in Washington, D.C., dating from the early 1900s, agreed. She reported a sound like pins or jacks coming from the ceiling. “I swore my upstairs neighbors were playing jacks, and they were two male recent grads. It seemed a very unlikely activity for them,” she said.
Hong Kong resident Andrea Lo said while she was living in an apartment dating from the 1980s on Hong Kong Island, she’d initially wondered if the sound of marbles and pins in her ceiling had a supernatural cause.
“I had a conversation with my friends who also experienced these noises in their apartments. This happens to so many of us in Hong Kong, we’d all thought we were living in haunted places until someone brought it up!” she said.
Some apartment dwellers have come up with less supernatural theories for the sounds they hear from above.
Eline Bakker, who lives in a 1950s building in Berlin, said: “I think it‘s got something to do with the old heater pipes in this building which have way too much air trapped in them. Sometimes, I wake up in the middle of the night convinced that there‘s someone in the apartment—that‘s how loud it gets.
“It was quickly built after the war and very rarely renovated since, so the old pipes have a lot of air trapped in them. It sounds like marbles or gurgling mostly—especially at the start of winter when we first start the heating.”
In an attempt to definitively debunk the things that go plonk and plink in the night, I contacted the American Institute of Physics. The organization recommended some experts.
Andy Piacsek, a scientist with the Acoustical Society of America, suggested the noises could be altering as they dissipate through the buildings, meaning the original sound could be very different to the ultimate noise of “marbles” or “pins” reported by so many people.
“The ‘rolling marbles’ problem sounds interesting and intriguing, partly because the answer probably combines different areas of acoustics; the generation of sound by water flow and possibly bubbles, as well as how that sound is radiated in a dwelling,” he said.
If the sound alters as it moves through a building, it means actual marbles and pins can’t be the root cause. But this makes pinpointing the origin even more challenging. “Plumbing is a good candidate,” Piacsek said. But the ‘dropped marble’ sound seems different from the ‘hammering’ sound I’m familiar with. If it involves water compressing trapped gas, somehow the water mass is decreasing—or the gas volume decreasing—for the frequency to increase as it does.”
In other words, water floods through a pipe, compressing the trapped air inside the pipe and creating the initial ‘dropped marble’ sound. As the water flows away or air dissipates, the sound resonates more loudly before fading away, imitating the sound of a dropped marble bouncing on the floor, then rolling across it.
Preston S Wilson, a professor in the Acoustics and Dynamic Systems & Control programs of the Walker Department of Mechanical Engineering at The University of Texas at Austin, suggested that hydraulic shock (commonly known as “water hammer”), could be the catalyst for the noise, but not the direct cause of it. Water hammer is a knocking noise in a water pipe that occurs when a tap is turned off briskly.
“Imagine a pipe running horizontally in the space between your ceiling and the floor of the unit above you,” said Wilson. “Someone, somewhere in the building, rapidly shuts off a faucet—or flushes the toilet, or an automatic valve in a dishwasher, etc. The water hammer effect causes the pipe to displace from its equilibrium position. It jerks up, then falls back down, and hits the nearby object—say, a beam in the ceiling.
“The pipe bounces back up, then falls back down, makes another sound and the cycle repeats a couple of times; each time, with diminishing energy. And after a few cycles, the motion is now too small to hit the object again, and the event is over.
“I think the marble dropping sound comes from the pipe being excited into motion from the water hammer effect, and then banging on another pipe, the floor, a beam, etc. It’s the sound of the pipe hitting the nearby object, rather than the sound of water running within the pipe,” added Wilson.
Wilson says whether the sound comes across as more like marbles or pins depends on several factors, such as how securely the pipe is attached to the building structure, how long the free run of the pipe is, what orientation it is in, and the exact nature of the water hammer.
“It seems that in some cases all the variables are right, such that the pipe moves in a way similar to the motion of a marble dropping (and bouncing) on a floor, hence there are some cases of water hammer that sound like this, and others that do not,” he said. “You can easily imagine a large variety of sounds that could come from this.”
Based on these hypotheses, it appears that if you hear these strange sounds in your apartment, you can rest assured you’re probably not actually losing your marbles—and neither are your neighbors.