droaning

Hi recently my car has started making an annoying droaning noise. It happened before so I changed the rear wheel bearings & cured it, so I stripped off the rear drums to inspect them, and one of the outer bearings had fallen apart. I changed both sides, but the noise is still there. Do you think...

started to notice an annoying droaning noise coming from my rear wheels. I've stripped the brakes down, greased up all the bearings, but the noise is still there. So I swapped my wheels, rear to front. The noise is slightly better, but still there. Any ideas? The tyres are nexen on the front...