The radius arm bushing may wear, causing a clunking or popping noise when driving over bumps. To repair, the bushings need to be replaced. Depending on the severity of the wear, the brackets may also need replacement. Driving with worn bushings will shorten tire life and cause tire cupping (uneven tire wear).Google+
Car Problem Reports
Ford Explorer Noise Over Bumps Due to Radius Arm Bushing Wear
Ford Explorer Problem
Average Mileage: 151,200 mi (106,000 mi - 238,000 mi)
Visitor, 1993 Ford Explorer, 125,000 mi
Jingling and clunking sound from front end passenger side; issue will disappear when vehicle is lifted, because pressure is being applied to radius arm. http://i.imgur.com/BIORJXP.png
Most shops will quote 3-4 hours for repair, as steps include removing the wheel, shock, spring, and various linkages per side, just to replace a $15-20 bushing. Beware of upsells, as the entire radius arm costs $100 per side; many places will not want to (understandably) do 4 hours of work to replace a smaller part like a bushing and would rather do entire assemblies.
1994 Explorer Sport 4x4--Clunks when shifting between gears (automatic) and when applying brakes. I've been told it needs bushings and U-Joints. I can't find a mechanic to fix it for me...must be very difficult to repair. I'm a woman--don't know much about this stuff.
Clunking sound will driving slow on uneven surfaces.
Visitor, 1994 Ford Explorer, 137,000 mi
Squeeking or clunking noise when hitting irregular spots on pavement. Radius arm bushing[s] were worn as well as one of the bushing mounting brackets. Replacement bushing kit for both sides was installed and one mounting bracket too worn to hold bushing was replaced.