The noise made when a car is drifting off the highway and it hits the grooves outside the lane intended to wake sleepy drivers before they crash.
It functions to keep sleepy, drunk, or ipod-fixed drivers on the road, and does a really good job. It probably saved my life.
When Nikhil started scrolling through artists on Steve's iPod, he was guided back onto the highway when he heard shhzzrrtttt.
Stan, Steve, Jack, and Pete had trouble sleeping on the car ride home, because they kept hearing shhzzrrtttt.