I was outside the hangar at 10:00 at night when i saw a yellow/orange light approaching from the west. initially, i thought it was the hospital helicopter but as it approached i did not see a landing light or any anti collison lights. as it passed in front of me at 2000 agl?, it had a very slight jet engine sound, appeared to ascend and disapeared in the cloudless sky toward the ne. it reminded me off an incoming meter with no trail or emmisions. five minutes later, two more came by heading in the same ne direstion, same yellow/orange color but with no sound, and obviously flying in formation. they also appeared to asend and disapeared into a cloudless sky. they were definately under intelligent control, and about the size of a penny at arms length. somewhat unnerved me so i immediately left the airport.