saw large diamond shaped craft fly almost directly over head at night (bright moon w/thin clouds) . Craft made humming sound that wasn't heard until it was almost overhead

I was with a friend standing near an  intersection of town near my home when my friend said " God, that's a big plane!". I looked  where she was pointing at the sky & saw two large bright white lights. I thought it was a large plane also but thought it was strange because the local airport was too small to handle airplanes bigger than a Piper Cub. I kept watching the lights & noticed that I could now see a red light between the 2 white lights. Couldn't hear any noise at this time. As the object flew almost overhead (it was cold that night with a bright moon w/thin kind of gauzey clouds) I could clearly see the shape of the object ,diamond shape with a white light at each point and a red light in the middle. It was at this time that I heard a humming sound coming from the object. The object was black on the bottom. The object flew over some trees & we couldn't see it anymore. I am a 42 year old woman w/a firm belief in UFOs.Have been very interested in the subject for many years.  I also read alot. Have a college education. The other witness was a friend of mine from high school (we were both about 20 years old at the time ) I don't know if she was interested in UFOs (never talked about the subject) but she was fairly intelligent.