Hi,
I had a rattle that happened under load, It could not be replicated with the bonnet up. The noise appeared to come from the front passengers side. I have owned the car a 2004 Cvt for the past 16 years so I Know the car pretty well as I am the only one who services it. I have been trying to track this down for the past 4 years. I checked nearly everything I could think of, exhaust heat shield, loose plastic etc. I narrowed it down to the air filter housing, new bolts installed, torqued up still the rattle. I eventually broke one of the housing bolts so as a temporary fix I cable tied it down. I drove it and found no rattle, it transpired that it was the White plastic stay clip that holds the bonnet arm in position when you close the bonnet, this was loose and would rattle against the air housing intake.
I have now cable tied the clip in place and Silence is golden once again.