Equilateral triangle in night sky

First off...I'm sorry to say I have no pictures of this event but please take a moment to read the story if you're familiar with aircraft.

Night before last, at about 10PM PDT a friend and myself were sitting outside talking at my Northern California home, and a large triangle formation of 3 lights passed overhead slowly.

It sounded like a jet although not like one I have ever heard, modulating in a mid-range frequency, I'd estimate at about 1-3kHz, it was a weird sound.

I live near two airfields, both former military bases that are still partially active, and I am used to seeing and hearing aircraft...this was like nothing I've ever observed.

The friend that saw it with me, is an ex Navy SEAL and an aeronautics buff, and he didn't know what it was, it actually left him a bit perplexed as he didn't see or hear it approaching, it seemed to just appear overhead, slightly to the East of our position and slowly moved to the West until it disappeared into the tree line/horizon.

My question is, does anyone know what kind of craft this may have been?

Thanks...over and out.

Check on youtube the Belgian Triangle event, the eye
witnesses put together the craft used in the TV show.

Check it out and tell us if there is a match.