What's this noise caused by?

[CraigyMc]

what's the "whump" noise caused by, when he changes down?

http://www.youtube.com/watch?v=OFLQAEiO7xo&fea...

[boredofmyoldname]

Blipping the throttle to match the revs a bit?

[powwerr]

It sounds to me its just the bass from the exhaust in the cabin as the revs match the downshift.