On 10-12-2016 at approximately 1145 hours, in post falls, idaho i heard a loud sonic boom, went out front door looking south and observed what appeared to be some type of large rectangular object tumbling end over end emitting a large amount of smoke (white, gray and yellowish in color) the smoke trail as it fell was about 4 to 5 times the width of a typical airliner contrail and in was going straight down toward the ground. at one point during this approximately 4 min fall, it appeared some type of engine maybe briefly came on and emitted what looked like what could be a jet engine trying to start or work but then it stopped and the trail became non symmetrical again. i got binoculars and tried to view it and while falling it intermittently reflected sunlight as it tumbled. the object appeared to be about the size of a very large military cargo plane or bigger, but more rectangular in shape. the object disappeared behind the mountains to the south of post falls and no doubt what ever it was hit the ground somewhere based on rate of fall and trajectory. after the object disappeared i called spokane faa tower and they said thanks but did not as any question or details.