2010 Audi A6 Quattro brake thumping
 

Brake pads seem to have life but the back thump like grinding. Check pads seemed fine and no brake light indicator... Please advise ... Thank you

I'd check the rear brakes again. Check the wear of the inside of the rotor. Sometimes the front sides will look fine but the back will have ditches and grooves from hell on them. The fronts that I just changed on my A8 looked fine but the backs were all to hell and looked horrible. Also most cars I've worked on do not have pad sensors on the back brakes, just the fronts. But still that doesn't mean anything if the pad is worn unevenly from a bad rotor face.