Sometimes carpets like a lot of materials stretch over time and lumps and ridges appear which can be unsightly, dangerous and can cause premature wear, if not treated it will result in the ridge or lump on your carpet becoming a hole. This is quite a common problem and doesn't necessarily mean that your carpet is or was defective or fitted badly. It could have been caused by numerous things, like heavy furniture being dragged over it, or not being cleaned correctly, or just the fact it has softened up.