Thumping from rear brakes, car was not driven for a month

I had surgery on my right achillies a month ago, in which time my car was not driven. Today it was driven and there was a thumping sound from the rear brakes, and I could also feel a light thumping in the brake pedal. Any Ideas of what this might be and how to resolve it? I had no brake problems prior to it sitting for a month.

It is possible there was a rust buildup and it will cure itself over time.

Chances are there is rust where the brakes were when it was not driven and now it needs some time and brake use to rub that rust off. You could have someone clean that rust off, but unless it is very heavy, it is not worth it and it will go away with use.