I have recently just got back disc and all round car new brake pads replaced. I have noticed a thump sound when hit a pot whole or slight bump in the road. Wonder what this could be at high speed don't hear anything. Car only done 42k looking for some advise please. 

I would say you should check all your bolts have been tightened up properly before doing anything else. Caliper and carrier bolts and wheel bolts. Once all those are checked and if all are tight, you might need to get a suspension inspection to check for a possible worn component.

 

Hope you get to the bottom of it soon.