I have a similarly odd story, but it happened a year ago.

I live 25 miles from LR AFB, the training center for C130s. Needless to say I can identify a C130 from its' engine noise as I've been seeing and hearing them daily all my life.

One night I heard a C130 sound, but it wasn't right at all. It was different altogether. I looked up and saw in the clear sky a C130 with no lights on. On each side of it was a helicopter with no lights on. Behind them was a helicopter that did have its' lights on. I'm fairly sure the choppers were all blackhawks. The sky was lit very well and the aircraft were easy to see. Their formation was very tight.