I have a 01 Kia Optima. The back wheel started making real bad noises, grinding when turning and in corners on the freeway. I kept thinking it was just the breaks and that I would get to it later. It does have the all wheel disc brakes.
Well come to find out that the hub in the rear is open bearing and the bearings were coming out. I have about 2/3 of them left. So I was driving on a prayer.

I took it off and went to the dealer and the dealer could have cared less that it was this way. The parts guy, who was a nice guy, was thinking that it just fell off. Which it could have, maybe....
So I bought a new one.... $200. Put it on and it sounds so much better.
But I looked at the other side and it was open bearing also. So it's a matter of time before the bearings just decide to shoot out of there.
If you have the 4 wheel disc brake you might look at this and see if yours is like that. The replacement part was at least sealed bearing.
Regards