so i have this problem and have tried EVERYthing.
the best fix i found was heavy grease like you'd use in CV joints. i'm actually using red lubro-moly. it's synthetic.
so it doesn't squeak but both back doors are incredibly hard to open.
i also have a weird problem where sometimes the passenger side doesn't open from the inside. even when the child lock is off.
i think i have to take these doors apart altogether and lube them up. but i'll wait until i put in new speakers...
