Rear Wheel Bearings

[Kisner]

What's the best way to determine if my 68 Mustang's rear wheel bearings need to be replaced? There's a low-pitched roaring sound (whoah, whoah, whoah) coming from the rear when I drive it. Does it at all speeds and seems to be relative to the wheels turning, but then the sound is drowned out by the engine when I get over 50. Wouldn't bet on it, but I think my transmission, drive shaft, U-joint, and rear axle are all fine. Also, last time I had the car jacked up, the rear driver's side wheel is real hard to spin and makes like a rubbing sound, while the passenger side spins fairly freely. Brakes are new and I'm pretty sure they're adjusted properly. It doesn't make any other unusual noises like grinding, rattling, etc. when driving or making turns. Thanks for any advice.