Mysterious vibrations - which sounded like a bass guitar and caused homes to shake - frightened Austin area residents over the weekend, prompting calls to 911.

"I heard a shaking noise - it sounded like wind hitting something," resident Denzell Hutchinson told ABC News affiliate KVUE. "I just thought it was wind blowing hard outside - until I went outside and there was no wind."

The vibrations started early Sunday morning. That's when fire crews arrived in the Harris Branch neighborhood of Austin and noticed homes vibrating. They eventually traced the mysterious vibrations back to the nearby Sunset Farms Landfill.

Landfill officials think a flare that burns off residual methane gas, a byproduct of the facility, may have shifted around because of storms the previous night.

"It's like a balloon: you vary the size and the way the air comes out of the opening, and it varies the pitch," Austin Fire Lt. Josh Portie told the Austin American Statesman.

"If you change the opening, it changes the sound, and that's exactly what happened."

Portie said the landfill operator had made adjustments to the damper on top of the flare and the vibration stopped.

There was never any danger related to the flare, he said.