I've just done a quick 5 minute journey, and felt all 4 hubs, and the rear drivers side is almost too hot to touch.
the disc surface doesn't look all shiny like the fronts, so by the looks of it, its a bearing issue.
The rumbling noise along with the dull thud type noise is there up to about 30-40mph, it doesn't disappear, but road noise increases, so it gets drowned out.
The noise started after I had finished the journey home from picking it up (approx 200 miles) I parked it up, then the next morning I pulled away, and its been there ever since, so I'm guessing I've cooked the bearing on the journey home from picking the car up, and what little grease was in it, has burnt away.
I don't suspect a bent alloy at all