These are pictures of RFI filters for power cords from devices that cause RFI into the power system of your house, and your Ham Radio Transceiver receives as noise that you hear sometimes. 

These are call common mode chokes using Amidon FT-240-77 Ferrite Toroidal Cores. About 12 turns of all conductors in a ac line cord are wound around the core. The plastic box is for housing, looks, and safety. Goop glue is use to hold the cores in place. These cores work very well between 1-30MHz.