Bus 42 Slowing down, Horn, Accelerating. 

*WEAR HEADPHONES, YOU WILL HEAR THE ENGINE AND ENGINE FAN A LOT BETTER*
2005 Blue Bird All American A3RE With a Cat C7.
Sounds absolutely amazing, I really miss this bus.
I noticed at a certain engine RPM, the engine fan locks on a certain speed. It also goes the same pitch as the engine which is really cool.