Maybe there's truth in the old worry about things going bump in the night.
Residents of West-Central Illinois, Northeast Missouri and beyond are reporting bumps, thuds and assorted noises that scientists say are another byproduct of this winter's weather.
One Camp Point resident described the sounds as similar to a tree limb falling, ice shifting off the roof or a bird hitting the picture window again.
Turns out that it might have been a frost quake, more formally known as cryoseism. Frost quakes happen when moisture in the ground suddenly freezes and expands. The soil or bedrock breaks like a brittle frozen pipe, generating noises that range from an earthquake-like rumble to sharp cracking sounds sometimes mistaken for falling trees.
Temperatures have been frigid, but occasional warm-ups have allowed for thawing, and the temperature swings have sometimes been abrupt.
"We have had several instances this year where we have had some pretty dramatic swings in temperature. It's not unusual for the temperature to fall 40 degrees," said Tom Williams, an associate professor in the geography department at Western Illinois University who specializes in weather forecasting.
"What that allows to happen is water in the ground -- either created because the soil starts to thaw out or you have a lot of melting snow that seeps into the ground -- suddenly freezes. We all know what happens to water when it freezes. It expands. You're getting all this expansion in the ground, and the ground is cracking."
That was the case last weekend in Missouri, where temperatures in the 40s on Saturday gave way to single-digit readings by Sunday night. The resulting noise prompted 911 calls in Marion and Ralls County, Mo., from concerned residents. Marion County 911 tweeted that loud booms caused by expanding ice, or ice quakes, may be occurring in the counties with no need to call 911 to make a report.
Chuck Herron of Paris, Mo., head the loud thud on Sunday, then another and another. It sounded like someone was dropping big snowballs on the roof of his home. The house is more than 100 years old and creaks, Herron told the Associated Press, but he had "never heard anything like that before."
Ice quakes are far more common in the northern and northeastern states and into Canada. Toronto residents reported hearing the quakes on Christmas Eve and again on New Year's Day. Residents in Fond du Lac County, Wis., heard the deep booms last month, with some reporting deep fissures left in their driveways from the quakes. Some reports indicate seeing distant flashing lights before or after an ice quake, possibly due to electrical changes when rocks are compressed.
"It's not something we would expect to see down here," Williams said. "You have the have the ability to have temperatures to get above freezing to thaw the ground followed by temperatures dropping below zero. We don't usually get those kinds of changes."
What Williams calls the worst winter in his 25 years of teaching at WIU has brought subzero temperatures that have frozen the ground, followed by warmer temperatures leading to a thaw -- and the snap, crackle and pop normally associated with breakfast time.
"At this point we've now had five significant snowfalls, six inches or more, with multiple Arctic outbreaks and subzero mornings," he said.
Conditions soon could be improving, compared to Thursday's high temperatures that were 30 degrees below normal.
"If we can get through another 10 days, it's going to change," Williams said. "How about the 50s? It would be well above normal."