hot rear wheel
there is a finite number of possibilities
car body rubbing on tire may cause rubber smell but not likely
running brake shoes or pads down to metal will do this but you would have heard the brake noise way before it welded in...hopefully...that is why disc brakes have wear tabs..
all rear wheels have wheel bearings which have a rubber bearing seal..should road salt or acid rain eat into t he seal and the bearing rusts we have friction,,easy to check
stuck parking brake or brake actuating cable may be rusted to the extent it freezes in the position where it will not properly release.
same may happen with rear disc brake pads if piston sticks in actuated position because the rubber brake hose is pinched closed..not likely as both rear caliper pistons would be effected..but..each rear caliber has steel brake lines that plumb to each caliber from the Tee fitting that the brake hose is connected to,,,.you may have a pinched brake line caused by running over some road hazard, thus locking a caliper piston in the actuated position
same can occur with brake shoe piston on non disc brake systems.
in all cases - heat is not a good sign and points to a friction condition. Some thing is causing this and inspection is in order..if car is rear wheel drive,,same as above can occur..if rear differential fluid is too low or not present you will hear major gear noise and bearing whine..
hope this helped