Just catching up on digests from the last couple days.  MY tapping from the rear was one of the curves in an exhaust header gently tapping on the engine carrier-support-thingy - varied in severity at idle vs underway.  Fresh new engine mounts brought up the engine/exhaust just a bit higher, eliminating the tapping completely.  Simply duck under the back with the engine running and see how close your various exhaust header curves are to the engine-carrying piece running longitudinally under the engine. 

Todd
91 Weekender

Date:    Tue, 5 Jan 2010 01:47:44 -0800
From:    PB <pbrattan@GMAIL.COM>
Subject: Re: Tapping under rear passenger wheel area

Thanks for your replies!  The mechanic diagnosed it as possible bad shocks.
He took it for a ride with me in the passenger seat (for the first time!)
He then stopped the van, got out, put his hands on something in the area I
described, and was able to produce the same noise by shaking it.  He said
that he routinely uses Bilstein shocks, but the ones I have are some kind of
non-Bilstein heavy duty shocks, which are not recommended.  I really don't
know anything about this stuff.  The mechanic also said that he couldn't be
sure of what the problem is until he puts the van on a lift, which is a good
thing.  He also said that by feeling the tires, he could tell that the
shocks should be replaced.  He said that when you run your fingers over the
treads, they should be smooth going either from left to right or from right
to left.  Mine are only smooth going from left to right.  Going from right
to left, they are rough.

I hope this all makes sense, and isn't just a "figment of the mechanic's
imagination!"

If it turns out to be axles, what can I expect that to cost in California?
That wouldn't be routine maintenance, would it?  I still have extended
warranty insurance until April 15.  I'm sure it wouldn't cover shocks,
because that's maintenance.  In the meantime, I have to wait to have this
problem fixed because I just dropped off my Jeep Liberty for brakes.  I'd be
marooned at home without transportation during the last week of my vacation
if I got the Vanagon fixed at the same time!  The mechanic told me it would
be safe if I drove it gently until I get my Jeep back.

Patti
90 Westy Automatic
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