I tell ya, its so bloody wierd, the haynes manuel describes the sound, and lists things from wheel bearing seals, wheel bearings, diff,diff bits etc, but one minute the noise is there, the next it dissapears, had a mate come around and we took it out for a spin, so he could listen to the noise, NOT A BLOODY MURMER  
parked up, went out the next day with the missus, 400yds after pulling away, that noise is back, next day, nothing  
which makes me think, it cant be serious   otherwise it would be there all the time 
  
Ive had both rear drums off, nothing loose in there, but did notice oil stain