I think with the PSE there is a quiet mode and a sport mode. In quiet mode (activated by an installed switch on the dash,) the baffle closes off the bypass. Perusing the various newsgroups, it seems that there are quite a few self-installs where the electronic baffle control is not connected, effectively leaving the PSE in sports mode full-time.
P.S.
In this case, there was loose parts:
http://www.renntech.org/forums/lofiversion/index.php/t5135.html
More info from Tool Pants:
http://www.renntech.org/forums/index.php?showtopic=302&#