Every night, I—like millions of others—put on a noise machine to help me sleep. Mine offers several types of noise: white, pink, green, and brown. I’ve noticed something strange, though. After about 30 minutes of the noise pumping into my head, I start to hear things. Sometimes it’s music, like a full orchestral score. Other times it’s people having a conversation just out of the range where I’d hear actual words. Occasionally, it sounds like my husband playing a video game.

So I do what most people would do when a random sound is keeping them up at night. I try to find it. I turn off the white noise and listen intently. Do I need my husband to turn the TV down? Should I text the neighbors to see if they’re alright? Is there, in fact, an entire orchestra playing a score in the alley below my window?

And of course, there never is.

The first time I googled this random noise-during-noise, I panicked. Apparently hearing things that aren’t there is referred to in the psych biz as auditory pareidolia, or auditory hallucinations, and is a hallmark of schizophrenia—and some experts say it requires a psychological check-up.

“Since there’s a higher probability of this phenomenon in those with psychological disorders, individuals should likely be evaluated by a mental health professional if they are hearing these hallucinations,” advises Ruth Reisman, an audiologist who focuses on rehabilitation with hearing technology. She also notes that research is divided on the topic, with some studies saying noise produces hallucinations and some saying it doesn’t.

But regardless, surely my therapist, who I’ve seen regularly for nearly a decade, would have picked up on any schizophrenic tendencies I may have. I’m a lot of things, but schizophrenic is not one of them. I’m just … hearing weird noises in fuzzy sounds.

Luckily for me and anyone else dealing with this particular affliction, it turns out there’s a perfectly normal reason you may hear random sounds in white noise (or any other continuous noise). It’s still called auditory pareidolia, but it’s on the pattern-matching end of the spectrum instead of the psychosis end. Simply put, your brain is trying to figure out what it’s hearing, so it’s filling in the gaps of the noise you’re listening to with a common sound.

“When you hear, your brain is a pattern-matching machine,” says Neil Bauman, CEO of the Center for Hearing Loss Help. “Everything I say, all my words, all the sounds, are in your brain, in your database. And as each sound comes in, your brain looks through its database to see if it’s got the same pattern of sound. If it does, it says, oh, I recognize that word.”

Even if it’s a word you don’t know—something in ancient Greek, for example—you’ll still recognize some letters and some sounds, and your mind will fill in the spaces in order to replicate a pattern you already know.

Any app or machine you listen to that produces a color of noise, like white, brown, pink, green, or otherwise, is based on an algorithm or a code. It’s not truly random—so you’ll get a little while of what seems like random noise, and then the sounds repeat. On the surface, it probably doesn’t seem like it. But your brain recognizes the pattern and tries to make sense of it, which leads to hearing noises that aren’t actually there.