What gives turbo's this sound?

There's a chance this could be a really dumb question but I hear trucks around here all the time and when their turbos blow off it sounds awesome. I'm not sure if it's just what they sound like after you turn the boost up a bit or if it's an aftermarket blow-off valve. My truck sounds nothing like the one in the video below when it blows off, it just sounds like a small whoosh of air.

Here is a good example of the sound I am talking about. This is the sound I like, it almost sounds like a bird chirping or someone whistling when they sleep.