Just heard the sound again today: an EZY 319 passing at around 3000-6000ft over my place.
Speedbrake-retraction would give an explanation to the WHOOoop, but not to the WHOOoooooOOOOP - unless it's common to retract and re-deploy the brakes in short order.
Last edited by Toryu; 25th Aug 2012 at 15:28.