I was at boeing plant making a delivery to bldg 40-51 on the south side at 11:04 pm. i was looking at east near the horizon, when i noticed what looked like 3 stars moving in a triangluar formation moving from west to east above the cascade mountains (that cannot be seen at night)which are about 30 to 40 miles away. i then noticed another 2 to 3 lights that also looked like stars in the night sky that was with that group in a triangluar formation. the lights then made a slow vertical circlular loop as one group, most became stationary. the lights then faded and disaappeared in about 15 seconds. the whole sighting was about 1 minute. it was hard to determine distance, but it looked like it was over the cascade mountains around the general area near mt glacier peak(an isolated mountain and sleeping volcano that had an ufo sighting on 5 oct 16). these lights did not have tell-tale signs of regular aircraft: strobe lights or red/green navigation lights nor do aircraft fly in loops in formation at night.