noise, vibration, light seen being chased by helicopters

It was 10:45 on 4-5-99. I had just gone to bed and was startled by a loud noise and vibration. We thought it was a boat in the river, but it got closer and louder. I got up and my son was still awake so we went outside to look. That's when we heard the sound of Bell Huey helicopters. Moving from the southwest to the southeast was a ball of light. It was traveling fast! Behind it and going really fast too were two large helicopters. It seemed that they were chasing the light object. We watched until they were out of sight and then went back inside. I returned to bed because I had to get up to go to work this morning. No sooner than I had got back in bed, I heard helicopters again. I jumped back up and ran back outside with my son and we saw two or three more huge helicopters going really fast from the southwest to the southeast.The object and the helicopters seemed to be traveling fairly low about 200 to 300 feet above the treeline. The object was about one third the size of the helicopters. After that I didn't hear anything anymore.