I just moved into an apartment for the first time and my neighbors below have problems with me walking. What should I do?

I just moved into an apartment. I'm living on the top floor, so I haven't heard anyone walking above me and do not know what it sounds like. On my second day in the apartment, a lady knocked on the door and asked me if I could try to walk more softly (I don't walk loudly by any means and the floor is carpeted). Tonight (my fourth night in the apartment) I was going to the kitchen to grab some food and my neighbors below me started hitting their ceiling loudly with something (probably a broomstick). What should I do?