Hi, I had stock blow off valve (disconecting tube, and mount a small filter like BMC system) in my car since 1000km to 5500km, and it sounds great, it makes a hard PCHIXX!!! when I off gas pedal and shift gear. Later I connect the original tube for a revision in the official alfa dealer and I go like this sice 5500km to 6000km. Yesterday I disconnect the tube and mount small filter etc. but now it sounds bad and weak, like pliiffffffffff.... and it is a sounda little more long. I don´t sense a big change in performance, I don´t sense if it´s like all days or it´s worse but the new sound scares me 
the sound it´s like the turbo charged less. wath dou you think? wath can this be? the turbine visualization in D mode is right, it show that the turbine loads 100%, etc. thanks!!
in past it sound like this videos
http://www.youtube.com/watch?v=2NIXB6hoLoc
http://www.youtube.com/watch?v=nQgZKxHMCtw
and now it sounds like this