Dark triangular object emitting "dread", searching for something, then challenges USAF base security.

the object came from the SE about 75 feet from our position, and about 35 feet above the ground, it had a triangle shape, no visible markings,, the object seemed to be extremely dark- flat black some what shimmery at the edges and at points on the surface of the object. There was a very deep drone hum, not really heard but felt, we didn't move as it seemed that if we made ourselves seen somethime may happen to us. As the craft passed in front to the NE and about30 yards from us a beam of brilliant whte light shot down to the ground from the (?) front of the craft, and began to sweep left to right down then up as if it were searching for something, When this light first hit the ground the was a disturbance of dust rising, and as it sweeped around you could see dust roiling up. We experienced an ill, nauseous, dread feeling. We continued to watch the object fade out of sight. The direction in which it was traveling would lead it towards a USAF TAC/MAC base. Soon afterward we felt eased of the "dread" and we about to leave when we noticed that the airbase had came alive, ie: search lights, sirens and military police vechiles ranging along the security fencewe saw this due to our being on a slight rise. We left in our car, and decided to check if the base was shut down, the main gate was closed and MPs were not allowing anyone to enter. The next day the word was that a coyote had set off the perimeter alarm.
Date may be approximate, although the witness does not indicate that fact.  Witness elects to remain totally anonymous.  PD