im pretty sure is the turbo making that sound i took my BOV of and when i booted my car it made that same high pitched noise. (slightly quieter)..im sure that is not a Bov making that noise. its the air making that sound and then slowing down to create the lesser sound. """Wastegate Chatter Myth There is a common myth in the automotive world about so called "wastegate chatter", a noise created on lifting off the throttle in a turbocharged car. The sound is commonly described as a chipmunk or a rattlesnake and is often stated incorrectly as being a result of the turbo's wastegate closing. The noise is in fact the air compressed by the turbo passing back through the compressor housing of the turbo after having hit the now closed throttle plate. A BOV (Blow Off Valve) will usually eliminate this noise, but in some cases, i.e. where the BOV doesn't open fast enough or is setup to only react to high boost, some chatter will remain. The chatter noise is very noticable on WRC Rally cars, where no BOV is allowed."""" http://www.youtube.com/watch?v=zSIf0IwdiK0