Body problems of the 2007 Cadillac CTS

I own a 2007 Cadillac Cts. On Monday, March 17th, at 5:45am, I was driving south bound on I-75. While driving with the cruise control on, traveling around 77 mph, at about mile marker 88, I heard a large thud noise like something hit the underbody of the vehicle. I then heard a loud metallic ringing noise and felt a vibration through the vehicle floor and steering wheel. I put my turn signal on to get over to the shoulder of the road. As I turned my head to the right to see if it was clear to get over, I noticed a large cloud of black smoke emitting from the back of the vehicle and could see an orange reflection of flames in the driver¿s door of the vehicle to the right of me. I got over to the shoulder at mile marker 87. I inspected the vehicle to see what was going on, I looked at the left side and didn¿t notice anything, then walked over to the right side of the vehicle (I was standing about 10 ft behind the vehicle on the right side) and noticed flames shooting out from under the engine compartment. I walked back about 50 feet and called 911 and reported the vehicle fire. The independence township sheriff¿s office responded about 5 minutes later and was going to attempt to put the fire out, but by that time the flames were shooting out of hood of the vehicle. The flames were about 4 ¿ 5 ft at that time and the officer decided not to attempt to put the fire out. Fire department showed up about 10 minutes after the sheriff was there and put the fire out. I had the vehicle towed to randy weiss gm dealer in fenton, michigan. Vehicle mileage ¿ 74,665 miles. Vehicle maintained either by lasco Ford in fenton michigan or al sierra in grand blanc michigan.