I've posted one thread on the 13 RAM 1500
crew with the 6.4' bed. Several other folks have commented their RAM's having a "twang", knock, or similar from different locations. Mine has been making a snap/knock/twang sound from the rear, especially at slow speed when going over uneven surfaces.
I finally had enough and spent some time tracking it down. It was the right rear coil spring; the foot of the coil didn't fit totally flat in the spring bucket on the axle. Each time I'd roll-over something, on the drop, the spring would "walk" like 1mm in the bucket, which would resonate through the coil, into the frame, and sound-off throughout the truck.
The fix is to support the frame, remove the right rear wheel, disconnect the lower shock mount, disconnect the rear stabilizer bar link, slowly lower the axle until the spring completely unloads from the mount, remove, clean the surface, use synthetic lube or something similar to create a thin film on the surface of the spring mount surface, reverse everything to install. No more twang.
This was a good time to do a brake inspection, rotate tires, and torque lug nuts to spec.