The iMac is a really bad ham radio operator's friend. I know, as I am ham (literally too) but it splatters RF radiation all over the place. Most of it comes from the video and horizontal refresh circuitry in the monitor components in the iMac.
My cube is virtually silent, as it does not have the monitor, obviously.
2000 iMacs had problems in the video circuits that causes wavy lines to appear when menus were selected or the mouse was clicked. Some users reported black lines going through the display.
Apple fixed the problem with OS 9.2, but the RF interference still remains.