Strange crafts with strange sound moving slowly towards Denver, CO.A strange object flew over us fairly slow, approx. 10,000 feet in the sky, with a sound that did not match the speed or distance from our location. It was very loud but was well past us by the time we heard it. It was very large and had white lights on both tips of what appeared to be the wing edges. Both witnesses saw a strange circular motion like a fan at the front of the craft and flew towards the Denver, CO, area. 30 minutes later 2 more flew over much higher but the same identical outline in the sky. Obviously the same type object with lights on both tips of wing. Both witnesses have never seen an object in the sky resembling these crafts and watch the sky most nights of the year.