Not sure what panel you're referring to. Picture?

 

I would suggest searching YouTube for a video on installing remote start for your year Camry. Most of those videos show how to get into that area below the steering wheel.

You're just looking for the part where they're taking that panel off. When you take the lower panel off there are 4 10mm bolts that hold the knee airbag module.

 

The panel that surrounds the airbag needs to come out first, and it is probably the only panel you'll need to remove if you're looking for something rattling. The airbag is fixed to the dash separately so it remains secure in the event it blows.

Anyway, that panel will require the removal of the small panel between the floor and the bottom of the dash near your left foot. That exposes a bolt at the bottom left of the big panel in front of your knees. There is another screw in a similar location on the bottom right. After removing the screw and the bolt, you can gently pull the panel until the clips along the top and around the airbag release. Hopefully that gets you far enough to find your rattle. Personally, I wouldn't touch the airbag at all.

 

Did you manage to figure out in the end what was rattling?