I have a 2002 Dodge Dakota 2WD 4.7 V8. When towing my 3100 lbs. pop up camper and have firewood in the bed I hear a horrible grinding noise when I accelerate and sounds like metal to metal grinding. When I take out the firewood I no longer hear the grinding noise. My Dakota is rated to tow around 5000 lbs to 5500 lbs. Could this be something with the U-Joints or driveshaft? I took it to a goodyear shop and they were clueless. This noise only occurs when I'm towing. I have a supersprings kit on the rear to help out with rear end sagging.

 

It could be anything. Yes check U Joints. Check out your brake system. It even may be a Bering in the axle system. OR even the shocks.