rattling sound from the rear right speaker ( OEM )?

well the speaker is probably blown it happens quite a bit with OEM speakers, I suggest pulling it out and checking for any small cracks in the speaker if you see one a good cheap but not permanent way would be to put some superglue or nail polish on the crack and it should keep you going a bit longer without the rattle

If the cone isn't torn, check the little wire braids that connect to the voice coil. Usually when they are overworked for a long time they will do like any wire bent back and forth. You might be able to fix that weak connection with a tiny bit of solder. You'll see clearly where it's weak and about to break off altogether. Be extra careful to not burn the speaker, or put so much solder on the braid that it can't flex anymore.

Some of the older Toyota speakers have a little silver diaphragm in the center to cover the top of the voice coil and keep dust and bugs from getting in jamming the thing up. Sometimes those covers can pop loose and rattle. Put it back in place with a tiny bit of krazyglue and don't glue the speaker coil so it can't move. Lastly, the most annoying thing that can happen is for a bug to fall in the speaker grill and die and rattle around on the speaker as it plays.

When you see the price Toyota charges for OEM speakers, you might want to yell. See if your local auto salvage has some good ones in a wreck. You might get lucky and find some premium ones for a few bucks.