Slow moving large triangle craft seen at close range, 1 white light in front 2 red in back, Low hum.

My mom, my brother and I saw a triangle shaped object 200ft-300ft in length moving at approx. 20 mph directly East to West down Gibraltar Rd in Fish Creek.  Object was first spotted when driving and was about 200ft in the air and 3/4 mile away.  After reaching our destination we observed the object as it approched from about 1/2 mile away.  The leading tip of the object had a white light on the underside while the 2 rear tips had red lights.  Before the object got 1/4 mile from us my brother got scared and ran inside to hide leaving my mother and me to witness the rest.  As it approched we saw an orange/white light in the center not as bright as the other 3.  As it passed directly overhead we could see lots of machanical 'busy-ness' underneath kind of like piping or electrical work however not in any traditional sense.  A very low hum could be heard almost below frequencies that can be detected by human ears.  We continued to watch until the object flew out of view behind a building.  The whole sighting lasted about 15 minutes the first 3 of which were while we were in the car.  The object remained at the same altitude and maintained constant velocity throughout the sighting.