Certainly more than ever, there are many, many sources of buzzing, noise on the good ol' AM band. Every time, seemingly there is an improvement to something, there is a bit of a detriment to the bnoise level of the AM radio band. Here are a few to be sure:
LED lights, fluorescent lighting, light dimmers, touch lights, power lines, wind turbines, flat screen TVs, motion detector lighting, Plasma TVs, cable TV near/above your shack.