Howdy
I wouldn't rule out shorebirds, though I can't think of a call like you describe. Plovers can be pretty noisy at night and I've heard yellowlegs spp. over Port Angeles well after dark, on very still nights this time of year.
One of my favorite birding memories: listening to the chip notes of passerines at night, when a strong autumn westerly had pushed southbound migrants out over North Carolina's Outer Banks. There was a steady stream for hours ... we couldn't see them, but there were hundreds. We tend not to think of all that nighttime activity.
Richard Schneider
Port Angeles