Was it an animal in distress? Heavy equipment tearing up concrete before dawn? A train accident?

Not that anyone in St. Paul could tell. But a distant, howling scraping sound woke people up about 4 a.m. this morning in St. Paul’s Highland Park and Mac-Groveland neighborhoods.

You can hear it here:

The sound echoed for miles through the city.

Ramsey County dispatchers initially thought it might have been demolition at the site of the former U.S. Bank offices near Highway 5, across the river from Fort Snelling. But they sent officers down to check it out and authorities now think it’s ice shifting on the Mississippi.

The river froze over in the gorge between St. Paul and Minneapolis during the recent cold weather, and it may have started breaking up as the weather warmed up last night.

Officials with the Army Corp of Engineers and the National Park Service, both of which have jurisdiction over the river, said they weren’t initially sure what the noise was, but they’re both listening and might be able to offer a more definitive explanation later.