Sounds like a bad cat or muffler to me.
 > Date: Mon, 18 Jul 2011 12:40:22 -0400
> From: sorkilmo@GMAIL.COM
> Subject: 2.1 engine clack or rattle
> To: vanagon@GERRY.VANAGON.COM
> 
> My engine (2.1 liter) just developed a clacking sound on the way to work.
> Will have more time to look at it later on. Was wondering if anyone had an
> idea of what might be the problem or what sorts of things too look at.
> 
> http://www.youtube.com/watch?v=MIRT14ojcLc
> 
> 
> Much thanks,
> Greg Sorkilmo
> 87' Hardtop
> Ottawa ON