Rattling noise inlet manifold - 2004 Toyota Corolla

Question edited to add full 'year make model'.
Question moved to model category.

The plenum is the pipes that balance the air from the air filter, to the Inlet Manifold. I don't see how it can 'rattle' as it is just an air chamber.

https://www.google.com/search?q=2002+Toyota+Camry+LE+plenum

There are a few things that can rattle, apart from something just being loose.
The water pump is definitely one.
It could be the idler pulley on the serpentine belt.
It could be the alternator.
It could be the AC Clutch

Here is a trick. Get a 5 foot length of plastic hose, like the sort used for wine making or the thin stuff used for the windshield washer. Put one end in your ear and use the other end to pinpoint where the rattle is coming from. Be VERY careful of moving or spinning parts.

Nissan had a problem with the exhaust bracket being cracked or broken

check that the heat defelector shrouds around the manifold are not cracked or broken on the mounting bolts. Check that you haven't a manifold gasket problem

what kind of noise? If it sounds like an exhaust leak. the 3400 motor has an issue with the manifold bolts breaking. Sometimes they get trapped in the cover and rattle. Does the noise get better as the car gets warmer? if so you need to replace some manifold bolts

if it sounds like a rattle thats your p.c.v. valve did you have a tune up latley probaly changed then . if so thats ok.

quick fix and cheap drain a quart of oil out of the motor then get a quart of LUCUS oil conditioner add to the motor oil. about (12-15 dollars) it worked to quite the little 2.0 that has always had a little lifter/valve noise,

I don't want to deviate from what you described but are you sure its not comming from the catalytic converter. sometimes the plate get loose and rattles

Try checking the heat shield on your exhaust system. You should have one over the manifold and one over your cat converter under the car.

This only happens when the Car is Cold???? It is the Exhaust Manifold. You need to Replace the Exhaust Manifold Gasket and check the Rest for Tightness.

had the same issue, had someone look and it seems the noise was caused by heat shield being loose covering exhaust system. Have that checked out.