After years of dedicated work, Goblin engineers have created an ultraquiet (silent) muffler for those pesky, loud engineering motorcycles!
Note: At some point in 2015 the extract location changed to the root WoW folder
Simply extract the downloaded file to
*World of Warcraft Directory*\
*World of Warcraft Directory*\Data\
or for some people
*World of Warcraft Directory*\Data\enUS\
Now you never have to hear another motorcycle sound ever! (Including possibly the Ulduar motorbike!)