Spotted strange pulsing light flying at a high rate of speed north to south.

Considering the proximity to the airport, I was hesitant to make this report.  However, being past this airport so many times, and never having seen anything that could explain this, I decided to.  It was a somewhat overcast night, and the lights of the town and airport were visible to my left as my girlfriend and I drove north on Interstate 95 towards Orono.  I noticed a flashing out of the corner of my eye and turned to see a white pulsing, circling flash moving VERY quickly across the sky in a southerly direction.  It pulsed intermittently, looking very much like a strobe but a bit slower.  It was out of site in only a few seconds, but the speed it moved at was not explainable by normal aircraft, nor was the strength of the light.  There was no plane attached to the light - just the light.  I saw a plane not a few minutes before that.  I told my girlfriend to look, but it was already out of site and she discounted it.  It was apparently close, only a few hundred feet up and it moved by flashing along, sort of in an incredibly gentle U-fashion to the south.  It was over a small line of trees and the town of Bangor.