Keep mine stock. Can't see spending a $1000 for an incremental noise bump. If its really really important to you just cut open the IS system pull out the stuffing & weld it closed.
2013 135is Cab JB4/ISO - 2011 335is JB4/ISO/BMS Flash - 2009 V-Star
2009 Ford Expedition EL 4X4 - 2003 Xterra 4X4 - 1998 Ranger 4X4 - FFR Cobra MK-IV work in progress