I was vexed by this symptom for a long time. Happened under the same
conditions you describe. But was not consistent. I could not reproduce it
by driving in a particular way. I believe it was the axel moving in and out
along its length axis. I could reproduce the heavy knocking sound by moving
the shaft by hand under the van. I believe the sound is the end of the axle
hitting the inside of the outer cv joint. Which is why it sounds like a
wheel bearing is the cause. It's a scary sound. Once I discovered this I
just stopped worrying about it and never found a cure.
Edward

On Tue, Oct 19, 2021, 4:21 PM Vanagon Man <t3vanagon@gmail.com> wrote:

> Howdy all-
> Hoping to get some input for things to look at in the search for a
> diagnosis….
>
> Over the course of a couple weeks, we noticed a knocking sound coming from
> the rear of our ‘88 Westy (2.1 WB)
>
> At the time, it occurred typically when turning, so the initial assumption
> (mechanic concurred) was the bearings needed to be replaced.
> While they did, it turns out that wasn’t the source of the sound (lucky
> there).
>
> It’s a variable knocking sound that happens under load when the
> accelerator is engaged.
> ATF is full, as is gear oil.
>
> Any suggestions are welcome!
>
> Cheers!
>
> Matt
> Missoula, MT
> ‘88 Westy, “Ragnar LoafBrick”
>