Given your descriptions I would put a knocking CV joint/axle at the top
of the list. Just about every other moving part turns too fast. Wear in
a CV joint can result in a rhythmic knocking sound. Assuming that is it
the good news is that it probably isn't an impending doom just yet and
isn't all that expensive to fix.

Mark

Dave Mcneely wrote:
> Mark, this may be the  most astute query anyone has made.  I did not time the frequency of the tapping sound, but did think about it, and thought that it should have been more frequent if it was one of the parts you mentioned or a bearing. But the sound itself did make me think it was engine, not chassis or drive system.   It actually was more on the order of a few times per second, rather than several tens of taps per second.  So it might be more likely to be a drive system component rather than an engine component?  I think I just need to get it in to a good Vanagon mechanic.  But to reproduce the conditions might require waiting till late spring, as I will not be where the van is until mid to late November, and don't expect warm weather any time real soon after that.  Dave
>
> ---- mark drillock <mdrillock@COX.NET> wrote:
>> What was the frequency of the sound you heard? At 3400 rpm the engine is
>> turning almost 60 times per second. Valves, lifters, pistons, and rods
>> are each stressed most at half that frequency, so 30 times per second.
>> At 45 mph CV joints/axles rotate at about 9 times per second.
>>
>> Mark
>
> --
> David McNeely
>