Plastic Panel On Top Of Display Center

Do you mean the plastic panel on the dash in front of the display? It covers the projector for the dash display. When you see your speedometer, etc. you are actually looking at a projected image.

 

By chance, could you be referring to this object:



If so, it's a Gen II-specific MFD sun shade. Ususally it is
held in place by small velcro strips along its edges.

More info at the PRIUSchat store.

 

I suspect he is referring to the speaker grill on top of the MFD.

 

It is held in with four pegs, two in the front and two in the rear. They have a wedge of plastic molded into them, such that once you press it in far enough it snaps to lock in place (the end of the wedge is a right angle). So I'm not sure if you need to press it towards the centre to release it or not. Probably. You may be able to release them with a thin flat blade screwdriver. I'd try using a piece of cardboard wedged under it to see if that stops the rattling first. No point in breaking it if there is a simpler solution. If the cardboard works then you can find something that will look ok wedged under it. Your dealer can show you a picture from the shop manual of the piece.