There have been previous threads on this subject. There has been a problem with collapsed pcv hoses on 'S' models.
http://www.mini2.com/forum/showthrea...threadid=40907 http://www.mini2.com/forum/faults-fixes/26574-whistling-supercharger-any-ideas.html
Also, I have notes on service measure M11-200-04 that affects 07/02 to 07/03 Cooper S models that replaces the PCV hose with a stiffer one. Date on the SM is 02/10/04 and it does not apply to ONE or COOPERs.