Bearing noises typically go away when you turn in one direction or the other, and sometimes upon braking.
A sticking caliper can roar, but usually you can smell it.
A worn out (to the metal) brake pad can roar, though this would tend to vary sound or pitch upon braking.
A bad alignment can cause a roar. Hit any potholes or curbs lately?
Any evidence in the tire wear pattern? Cupping or edge wear?
If you have any doubts about the noise being engine vs. running gear, the best way to discern is to get it up to speed on the highway, then pop it into neutral and see if the noise stops.
I once had a noisy water pump when I was certain it must be a wheel bearing...
Best of luck.
1986 300E 5-Speed 240k mi.