Stop Marks Research
This problem occurs when manufacturing stops momentarily or has a momentary vibration in the beam or creel. If the machine actually stops there will be a missing row of yarns; if it is due to tension variation, then a row of tufts may be lower than the surrounding yarns. Either way a width wise line is left in the carpet. This line may be the only line of its type in the carpet or there could be others at irregular distances from each other. In most cases this problem cannot be fixed and the real issue that may be addressed is, how offensive is the problem.
The pictures below shows the problem to be due to a tension variation.
Close Up
There is an inspection report associated with these pictures.