Pete on the Boxertrix.com site posted these informative instructions on curing the throttle body rattle, fixed for a few quid too. His was a 2004 1100S which appears to be the same as the 1150GS going by the part numbers
http://www.boxertrix.com/phpBB2/viewtopic.php?f=14&t=23953&p=196500#p196500
http://www.boxertrix.com/phpBB2/viewtopic.php?f=14&t=23953&p=196500#p196500