Hi,
I own a 2008 Ram 3500/6.7 TurboDiesel and recently my truck started howling whenever I accelerate. It's the loudest when I'm going 60km/h and 95km/h. My mechanic told me it's probably the rear differential. He took a look at it and found that a part was loose. He tightened it, but the noise is still there. He said it didn't sound like something I should be worried about and that I should come back if it becomes louder changes in pitch. Also, when I'm stopping, just before I come to a still stand, there's a noise that almost sounds like a yawn. It's there and then it just becomes quieter and disappears.
Tomorrow I'm going down into the States again, so if I need to change something, I can do it there.
Anyone know what this is?

 

If the part that was loose was the pinion nut then you do have a problem.

Did he check the U-joints for binding? Disconnect drive shaft and check u-joints first. Check for any roughness or binding in pinion bearings while drive shaft is off. Pull the diff cover check for excessive metal particles on magnet. Check carrier for any side play in bearings. Check backlash and pattern check on gears. Fluid color for overheating. Run truck on lift in gear and listen for any noises with mechanics Stethoscope.

 

Yeah, the u-joints were fine. There were no metal particles on the magnet. I will take a look at all the other things you mentioned. Thank you!