Another notable feature of Bolliger and Mabillard roller coasters is that they make use of box-section track: the running rails for the coaster are connected to a box-section spine, as opposed to a circular spine used by many other manufacturers. Because of this, when a train travels round the track it creates a distinctive "roar", which is unique to this style of track. Some B&M coasters, such as Talon at Dorney Park & Wildwater Kingdom and Dueling Dragons at Islands of Adventure, have their track filled with sand to reduce this noise, resulting in an unusually quiet and hollow sound.
Here ya go... Taken from <a href='http://en.wikipedia.org/wiki/Bolliger_&_Mabillard' target='_blank'>Bolliger & Mabillard on Wikipedia</a>

