Authorities in St. Paul are looking into the source of a mysterious noise that awakened residents of neighborhoods near the Mississippi River before dawn Thursday.
Minnesota Public Radio reports Ramsey County dispatchers started getting calls around 4 a.m. from people variously describing it as a howling or scraping sound. Theories ranged from an animal in distress to demolition equipment to a train accident.
MPR posted this audio clip of the sound:
An employee with the county's emergency communications center tells the Pioneer Press 10 callers offered guesses such as an organ, whales, or a horn blowing.
Police officers checked the areas in the Highland Park and Macalaster-Groveland neighborhoods, but found nothing. Its public information officer says the department continues investigating.
MPR says the National Park Service and Army Corps of Engineers are also looking into the mystery.
One of the leading theories is that shifting ice may be the culprit. Temperatures reached their warmest level in more than a week early Thursday, the Pioneer Press notes.
The climate was also tapped as the likely source of another mystery sound this winter when "frost quakes" were reported in western Wisconsin. In those cases, loud cracking noises reportedly shook homes.