noise coming from left rear

I've been noticing a cyclical noise eminating from the rear driveline on my '93. Today I pinpointed the sound by jacking up the rear and putting it in drive. There's a howling / whirring coming from the left rear axle (at the brake drum) that is much more pronounced when the weight is off the wheels. Can anyone advise what this might be so I have a clue when I take it in to have it diagnosed? Thanks

First guess would be a wheel bearing.

I´ve never had much trouble out fo my wheel bearings, but every XJ (or YJ) I´ve had (with the D35) with more than 125,000, has had some play in the carrier bearings. If it gets worse in reverse than in forward gears, the carrier bearings are a possiblilty.