Rodeo, 2000, 3.2L V6:  At 1800-2000 RPMs there is a rattle in th
exhaust system. It sounds like a lose heat shield, but the truck ha
been up on a lift to check heat shields and none are lose.  Whe
driving with another person and the passenger wondow open (th
passenger can really hear the rattle), it seems to be from the area o
the cat converter or a vibration in the passenger floor. Also whe
tapping the exhust pipe around the cat converter it sounds as i
something is lose or free inside the cat converter.  A mechnic ha
suggested that the front exhaust pipes maybe double wall constructio
and the inner wall has broken free from the mounting point and i
vibrating

Note: Mileage is 98
Tapping on the exhaust pipe is not enoug
i would grab the end of the exhaust pipe and shake it sid
to side and even in a up and down motion and listen for nois
the other posibility is a  catalytic converter thats broken up on the insid
you"l need to take it right off the exhaust and check both ends i had t
replace one years ago on a volkswagon passat i owned had the same problem you
describing took it off and sure enough found it in broken pieces on the insid
put an aftermarket one on & problem resolved

--
johnin

I had a similar problem on a Toyota.  My mechanic used some chemical to
"de-carbonize" the exhaust system.  Sorry I don't know what it was or how it
was applied.

Because you hear a noise near the catalytic converter, it may be the cat
itself.  I don't know how modern cats work, but the ones from the '80s had a
small platinum wire that was the catalyst and they could come loose at one
end.  As it is an emmissions related part it may be covered under warranty
even if the rest of the vehicle isn't.  Thought 6 years and almost 100K
miles may be beyond mandated emissions warranty.