The truck has less than 20k miles on it and about 3 weeks ago, after a day of pulling a 4k lb or so trailer, I started noticing this creaking noise coming from the rear of the truck. It only makes this noise under acceleration of some sort. Whenever the rotation direction of the drive shaft changes and is under accel, it makes the noise. That's what it seems like to me anyways. I'm not too sure so I figured I'd see if anyone had any ideas as to what this noise is.