Wow, after puzzling for so many nights over my mystery neighborhood flier, 10 minutes on this list and I have my answer. It's a Caspian Tern - Joe in Bellingham and Stuart in Seattle should get a prize for quickest deduction - I'm amazed! There's a sound byte on this page which reproduces the call exactly:

http://www.mbr-pwrc.usgs.gov/id/framlst/i0640id.html

Thank you all so much for your help! I'm thrilled!

Ren?e Gagnon
Everett, WA
rs.gagnon at comcast.net