Every so often at night I here a roaring sound in the sky like a rocket engine over head. It starts out faint then grows in intensity, reach's a crescendo then fades away. The sound does not move its stationary. I cannot see anything in the sky, it is not an aircraft or helicopter, I live in a rural area. Nothing that could make such a racket, no factory's, no other industry just trees and horses. I have googled this for years but I find nothing that can explain it. Hoping to find some real info.