Chevrolet Repair: 98 Astro van rattle, astro van, heat shield

Question
my 1998 astro van has developed a short (1-2 sec in duration)metalic rattle around or below engine at startup (actually about 3 sec after start up when the engine idle increases slightly) and then goes away.  It reapears briefly whenever speed decreases to about 15 mph but never last longer than a sec or two.  It's like some sort of cavitation.  Any ideas and is it serious, we're leaving for vacation and no time to get it looked at here (since we leave tomorrow - Sun and no shop is open).  I could get it looked at out of town but would prefer to go to our regular shop upon return if it can wait....  Any suggestions would be appreciated.

Answer
Hi David,

Without hearing it, I have to strongly suspect it is the catalytic converter.  This happens with age and simply means the brick inside the CAT is loose from age, or it is the heat shield around it that has become loose from normal rust.  Neither one of the problems is nothing more than an annoyance.  Go on your vacation and pay no attention to the rattle.  You can wait until you return.  Even then you can wait.  

C J S