Aural warning during autostart 747-400
I hope this is the correct forum for this question.
What would cause an aural warning (like "whoop-whoop-whoop" one time) when an engine is autostarted on a 747-400, either when the start switch is pulled or when the fuel cutoff is set to run? I can't find anything about it in the operations manual. I thought maybe yaw damper settings had something to do with it, but that doesn't seem to matter. Or maybe duct pressure. I don't know. Maybe the real aircraft doesn't ever sound such a warning (?).