Back Right side brake area Issues.

[DatSRBoi]

Ok WHen I drive I feel this rocking back and forth and the same time rubbing sound especially at higher speed and braking that It is the loudest. But when I tooked off the rim and look, the brakes and all bolts I could see are tight and nothing is loose. Then I notice the brake rotors were loose, but figure thats how it was. It wasnt until I putted the tires on and rocked it that I notice that the tires shook back and forth but the brakes and shocks and etc wasnt moving. My quoestion is could it be bearings? I couldnt take off the brake rotors to look behind and check...Can someone help me and how much It would cost?