Often a "thunk" can be a part of the exhaust system hitting another part of the van.
Mine sometimes does it on start up.
Anthony'89 Syncro GL (Hidalgo)

--- On Fri, 11/26/10, Michael <michael@JAMHOME.US> wrote:

From: Michael <michael@JAMHOME.US>
Subject: random "thunk" while sitting at idle
To: vanagon@GERRY.VANAGON.COM
Date: Friday, November 26, 2010, 3:05 PM

It happened again this morning.� I'm sitting at a stoplight with the van
just idling.� Then I hear a "thunk."� Nothing changes in
the performance or operation of my van.� But every few days I hear it
again.� Thunk.

The sound seems to be coming from the
back.

What suggestions do you have for investigating this
mystery sound?
Or have you BTDT and have a suggestion for what it is?

--
� ���Michael Rasmussen

http://www.jamhome.us/
 Be Appropriate && Follow Your Curiosity