My 2005 Rio has a constant whirring sound like something is rubbing and when I get to higher speeds the sound increases and the wheel sometimes shakes or will shift left or right. Also recently when I reverse, there is a crunching sounds emitting from the rear.
Sounds likek you either have a piece of hardware that has come loose in the drum or more likely your suspension has a bushing or ball joint that is about to fall out. There is a bushing called a Trailing Arm Bushing that when it gives out it will let the rear end go all over the place and will feel vbery unstable.
If none of that applies, the wheel bearing may be gone or it needs new brake shoes.