These stains are always annoying and we have these stains everywhere where there is a lot of walking and sitting. We also have carpets there, but they have such a rough underside and do not slip.
I find wall-to-wall carpet in the hallway, that is not an inexpensive option. That is also the area that is used the most and also stressed. Then putting a carpet on top of it, that just doesn’t work at all. Either new wall-to-wall carpet or just a carpet.
We have done that before as well. We put a carpet on the wooden floor and placed a rug on top of it. Never again, because the bottom carpet had started to smell musty. From these experiences, it is now clear to buy a new carpet and remove the old one.
I don’t think that is an option. Just lay a new carpet here if it absolutely has to be a carpet. Nothing else will work and it doesn’t look good either.
We have done that once before. On the floorboards, we have wall-to-wall carpeting and on top of that, we laid a rug. Never again, because the bottom carpet had started to smell musty.
From these experiences, it is now clear to buy a new carpet and remove the old one.
If it smells musty, then moisture must be getting in somehow. It doesn’t just get musty on its own. Or something like water was spilled, then that can happen.