I believe the sound comes from an electric motor that is designed to push clean air through the exhaust system at startup. The electric motor should shut off in about 30 seconds.

 

Here are the culprits (the secondary pulsed air system):

-First installed in the left front of the car


-Second... of them on the garage floor where they belong! How dare Honda put an emission thingy where I want to put a filter for a custom cold air intake!!


Not that I am against emmision control devices... they just mostly seem to be in my way. As for my Back Yard Special catalyst straight pipe... no comment!