Residents across several Cincinnati neighborhoods say a mysterious, siren-like noise has been disrupting their lives for weeks—keeping families awake, unsettling children, and fueling growing anxiety as officials search for answers.

The unexplained sound, described as a “whirring” or “oscillating” hum that rises and falls in pitch, has been reported in Northside, Clifton, and Camp Washington since December. According to residents, the noise is most noticeable late at night, often beginning around 10 p.m. and sometimes lasting until the early morning hours.

Residents echoed those concerns. Northside resident Brendan Marcum described the sound as unnatural and deeply unsettling. “It feels like a foreign sound,” he said. “Some nights it’s louder, some nights it’s quieter, but once you hear it, you can’t ignore it.”

As official explanations remain unclear, speculation has exploded online. Hundreds of residents have shared theories on social media and Reddit, ranging from industrial equipment to biblical or supernatural causes. One frequently cited possibility is River Metals Recycling, a local facility known for loud mechanical operations. Some residents claim the plant’s metal shredder may be responsible, though others note the facility has operated for years without producing anything like the current noise.

City officials have not confirmed the source and are urging residents to document disturbances. Cincinnati recommends that anyone experiencing the noise report it to 311, the city’s non-emergency service line, to help officials identify patterns and investigate potential causes.

For now, the sound remains a mystery—one that continues to disrupt sleep, heighten anxiety, and leave residents searching for reassurance that the eerie nighttime hum will eventually come to an end.