All you can do is jack it up and spin the wheels, hopefully the offender will sound off, if that doesn't work after driving some distance without braking have you tried pulling itno a layby, braking to halt on the handbrake only and feeling the bearing areas...hopefully one will be significantly warmer.

Had a similar unkown bearing on my old mate's Pug 305 years ago, it sounded worse cornering one way but was quiet and smooth spinning free by hand, so he changed the side that took the weight...not so, it turned out to be just as bad and it was the inside bearing of the other side that was gone after all, sometimes it just happens like that.