I know that about 5 seconds after I post this thread the next reply will take the piss,...
... but I'm genuinely baffled about this mystery and would love to know what is going on.
We moved into our new build house about 4/5yrs ago. The house was newly carpeted in every room except the kitchen where we had laminate floor.
Everything has been fine with the carpet. The material seems to standing up to general wear and tear pretty good.
Gets vacuumed every week and the occasional spill removed with carpet shampoo.
About 3 months ago I noticed a strange mark on the carpet near to a wall.
The stain pattern is very uniformed and defined. 3 parallel lines (like sergeant stripes). Dark in colour,... almost oily in texture.
Could not removed the stain with any amount of carpet cleaner or elbow grease.
Then more and more started appearing. Sometimes in different orientations, but always 3 parallel lines together.
Now they've appeared in every room in the house and in areas that nobody can possiblly get to,... like behind the TV and under the Christmas tree.
Mostly these marks accumulate near the edges of rooms, beside skirting boards, under radiators and besides the bed.
We never wear shoes indoors, so that rules that one out.
A guy at work told me of a similar situation (think he'd seen this on tv, rather experience it first hand) where some strange patterns had appeared on walls in a house.
The pattens kinda resembled large symmetrical snow flakes but in a dark colour. After much consideration, a possible (and plausible) reason behind this was due to old nails being hit into the plaster walls with a hammer (presumably during construction). The act of hitting the nails hard with a hammer, rather than using a screw, coursed the nail to magnetize. Then as time passed small amounts of iron/metal fragments in the atmosphere were drawn towards the magnetized nails leaving these strange patterns on the outside of the wall.
Now I'm not saying this is what I have in my house,... probably not even similar,.... but I do wonder if there is an scientific answer to what is going on?