I was returning home yesterday from a camping trip pulling my 5000# camper. My wife had her window down for a change (we normally run A/C). Every time I would let off and clutch it, I would hear the turbo whistling as it spun down. COOL. :ro) I didn't think you could hear it with the stock intake/exhaust. Kinda makes me want to put an aftermarket exhaust on to make it louder, maybe someday. I just thought that this was cool, and it sounded great. Kinda hard to hear from the driver's side, but when there was a guardrail or something beside the truck to reflect the sound, it was very noticable. COOL!:ro)

With exhaust and aftermarket intake you won't believe the whistle, I have other diesel truck owners looking at me all the time, my techs tell me they can hear me coming before I come under the overpass by my shop! :)