Here's a picture of my car's backbox. I havent got the secondary box that the ST's original system has so at motorway speeds it does get very "boomy" but like you say if I'm careful on the throttle I can even it out a little.



The only video clips I have of it are of my car on a rolling road and the fan they used kinda gets in the way but you get an idea of what its like from the outside at least.

http://www.youtube.com/watch?v=XNQ8u8DGVro