I think a more common rattle is the tin shroud over the muffler.  The spot
welds come loose or rust out and it rattles against the muffler.

>From: Mike Collum <collum@VERIZON.NET>
>Reply-To: Mike Collum <collum@VERIZON.NET>
>To: vanagon@GERRY.VANAGON.COM
>Subject: Re: Rattle in catalytic converter? 88 Vanagon
>Date: Mon, 16 Jan 2006 11:25:53 -0500
>
>John Graham wrote:
><snip>
>I noticed that I have a rattle in the back end for a
>>while after starting from cold that sounds like sheetmetal or tin.
><snip>
>
>
>It's likely that the honeycomb inside the CAT is broken.  The little
>pieces could even clog the muffler.
>
>You'll have to get your own new bolts when you replace the CAT as they
>don't come with the CAT or the gaskets.
>
>Mike