A sonic boom shook homes across parts of Denton County on Wednesday morning.

People from Aubrey, Sanger, Krum and Gainesville called FOX4 about the loud and reverberating noise about 11 a.m. on Wednesday. Some people said it had even knocked items off of walls.

It turns out the boom was caused by test planes.

Lockheed Martin said it had two supersonic aircrafts running test flights over that area of North Texas.