I think you're referring to a blowoff valve. Usually these are placed in an intercooler line to vent pressure when the throttle is released. The vacuum opens a valve and vents the pressure. That way, built up pressure from the turbo doesn't work against you to slow down the turbo impeller and the turbo doesn't have to work against existing pressure to spool up again (think of shifting a manual tranny car). You gas it and the turbo spools up and builds pressure, you let of (well, usually) to shift and the turbo works against itself, the shift is made and you gas it again and the turbo has to overcome whatever pressure is existing to spool up again.
The blowoff valve vents pressure either to the atmosphere (hissssss) or to the intake (stealth). A common bov (blowoff valve) is obtained from an eclipse and incorporated into intercooler lines.
If you're not running an intercooler, I'm not sure where you might install the "noisemaker".
Dan