Heehaw heehaw heehaw heehaw...clunkity clunk clunk...heehaw heehaw heehaw heehaw...
What the...? Does that sound familiar? Just what the heck is that noise? If you've got that sound coming from the front end of your Vanagon when you go over bumps (or when you jump up and down on the front bumper), you've probably got an issue with your front suspension upper control arm bushings.
The upper control arm (UCA, or sometimes known as A-Arm) is the part of the suspension that connects to the body at one end, and at the other end connects to the upper ball joint at the top of the spindle, around which the front wheel rotates. As your wheel goes over bumps, the UCA has to go up and down relative to the body of the vehicle. The UCA is one of the components that attaches the spindle to the body. Where the UCA attaches to the body, there are two bushings. The purpose of these bushings is to allow the arm to rotate up and down and to absorb road vibration.
In the old days, upper control arm bushings were not really bushings, but just vulcanized rubber mounts. For the control arm to rotate around the pivot point, the rubber would just flex. The UCA bushing design used on Vanagons is much more sophisticated. It is actually a rubber mount—like in the old days—surrounded by a real bushing. The rubber component absorbs vibration, as in a traditional bushing. The rubber is vulcanized to the inner part of the bushing, which is bolted to the body. What is different about the bushings used in Vanagons is that there is a thin layer of slippery plastic between the rubber and the outer part of the bushing that is connected to the arm itself. So, over small bumps or rough road irregularities, the rubber does all the work. Over larger bumps—where a higher degree of control arm movement is required—the plastic material allows for smooth slipping. If the bushings used are high-quality (and installed correctly), they give 100,000+ miles of smooth, quiet service. However, replacement bushing quality is not nearly as good as the original part, and the complexity of the bushing makes improper installation very common.
There are many different brands of OEM-design-style upper control arm bushings available for the Vanagon (and at least one other non-OEM-style offering in addition to the GoWesty option). All of the OEM-type look basically the same as the original... on the outside! As an experiment, we purchased one of each brand and cut them in half, along with the original VW part. The internal design varied from closely resembling the genuine VW-Audi design to basically being a wolf in sheep's clothing. The cost of the various brands of the non-genuine part varies as much as 400%—but all are still way more economical than the OEM VW part—when it was available. If you decide to replace your worn bushings with the same OEM-design style, make sure you are getting the right bushing: If it doesn't come from GoWesty, all bets are off! 
So, besides the pitfall of part quality, there are several ways to screw up the installation of the OEM design bushing.
The first way that the installation can go wrong is if the bushing is not pressed in straight, resulting in too much force being exerted. The bushing's metal outer casting is actually quite thin and can easily deform. When it does deform, it is junk and has to be tossed. However, an untrained eye will not catch the mistake, and then after a short while... heehaw heehaw heehaw.
The next most common way an installation can go awry is specific to 2WD upper control arms. 2WD arms are made of stamped steel sheets. 4WD arms are crafted from a thicker, forged design. To retain the bushing in the 2WD stamped arm, it is necessary to use a small weld. It's a very small spot weld that is required, followed by a quick quench in water right away before the plastic part of the bushing melts. If your weld is too large, or if you do not quench it quickly enough... heehaw heehaw heehaw.
The upper control arms on 4WD models is a completely different, stronger design. The area where the bushing mounts is much thicker and provides a much better press fit, so no welding is required. However, the stronger arm is far more rigid than the stamped steel 2WD A-arm. So, on 4WD models it is critical to use camber adjustment and eccentric washers of the correct thickness. It is not widely known that these washers are available in varying thicknesses for this exact purpose. The ones that were used with the old bushings may not be the correct thickness for the new bushings. If the correct thickness is not chosen, the rigid A-arm will cause undue strain on the bushings when the pivot bolt is tightened, and in short order... heehaw heehaw heehaw.
The ultimate choice is to switch to the GoWesty-designed version:
We did away entirely with any rubber component. You would think that would result in more road noise... and maybe it actually does. But we're talking about a Vanagon here. If this design is, indeed, allowing more road noise to be transmitted to the body, it is totally inaudible to the human ear. Our bushing solution also requires no welding. The outer race of our design is very sturdy, much thicker than the original, and crafted of stainless steel, which means that 1) it will not deform when pressed into place, 2) it does not require any spot weld to hold it there, and 3) it will never rust! The inner race is made of stainless steel, too. The bushing material we use is the key to the entire system. Others have tried to come up with a non-rubber solution for this application, but they ended up designing the whole system around the wrong bushing material. We employ Delrin AF, which is a DuPont trade name, which is a mixture of two other DuPont trade names: regular Delrin (polyoxymethylene) and Tephlon (polytetraflouroethylen or "PTFE"). It is extremely durable, strong, and slippery. The result: practically infinite life and no lubrication required ever. These will be the last bushings you install!
No more heehaw heehaw heehaw again... ever!
Note: there is another item in this UCA area that can easily be mistaken for UCA busing noise: the upper shock mount. Specifically, the steel spacer that runs thought the rubber mounts. This spacer can create a very similar noises. To remove this from a possibility, you can simply pry between the rubber mount and body and squire some lubricant in there. If the noise goes away: that is your problem!