Silly Question About Noise

[maxman]

2006 6.0 What is the noise that goes away when I let off the throttle at cruising speed? This is a normal sound that I hear all the time but when I let off the throttle it goes away and returns after coasting for awhile, I don't corelate it with the transmission downshifting, it sound like normal diesel clatter.but the engine is so quiet at coasting idle, then with just a tiny application of throttle the noise returns......I know this is silly but out of curiosity I just wanna know what is goin on........thanks

 

[Zookie400]

its the injector solenoids....when you are engine braking they stop firing, and when the rpm's come down close to idle speed, or you hit the throttle, they turn on again.
it saves fuel, barely.