Have you ever moved your drapes back so you could vacuum underneath them, or tried to tie your drapes back and realized there’s black wavy lines where the bottoms of your draperies used to rest? These unfortunately are once again the notorious filtration lines!
Take a look behind where your drapes used to lie and see if there’s an air vent behind them. If so this is one of the main sources of your problem. Your drapes have been catching all of the air that has been filled with junk not caught by the air filter(either because its not in right or you haven’t replaced them in forever.) and has been pushing that air under the bottom of your drapes through the carpet fibers.
This once again is acting like and air filter and if your drapes are left in that position for quite some time these marks will become permanent.The only way we can think of that could prevent these is to tie your drapes back in the corners of your windows, or to vacuum at least once a week under where your drapes lie. You can also have us come in and try to remove them with our machinery because they are more accessible than the ones that are buried in the wall corner apply s of your home, but once again we aren’t promising anything.