Hi all

Just curious. We have our TV under a reinforced concrete staircase. Yesterday evening the TV picture tube gathered some magnetic flux (green colored patches) towards the top of the picture tube. Most of the patches are now gone except one at the top left corner, hopefully it will go away too.

What could be the reason? One thing I have in mind is that the concrete staircase has a lot of metal in it (for the last 23 years, staircase, the TV is new :)). Anything in the Earth's magnetic field affect the metal inside and thus the picture tube?