ok, ive had this happen three times already, i get into my truck in the morning and let my pumps fill up with fuel for a couple seconds and crank it up and within 3 or 4 seconds my truck makes a really LOUD POP but nothing happens, it runs fine and i dont have any problems, but being so loud im worried somthing is going to break. it sounds like its coming from the passenger side of the engine the first two times but the third time it sounded like it came from trany?!? and another time i had my key just turned forward but didnt have my truck running and it sounded like i had some kind of whistle or air leak or vibration coming kinda from my radiator but it went away within 5 minutes... maybe it has something to do with the loud pop. any answers????

 

Possible that you are hearing the a/c compressor engaging. No technical explanation as to why, but the CTD equipped trucks have had a loud a/c engagement for a long time. My 01 will do it, but it's not as noticable as the common rail trucks.