If one reads about the LP record production process from start to end, you end up amazed that any LP sounds acceptable. There are just a lot of points in the process for quality to deteriorate.
A lacquer coated metal master is cut, which is electroplated to form a negative, which in turn is used to make a new all metal mother, which then is electroplated again to make the negative stamper plates.
Impurities in the plating chemicals, dust, or sloppy handling at any stage can cause noise in the stamped record.
Stampers can also be used past their prime. Stampers also do not typically fail instantaneously, so LPs made toward the end of the stamper's life will not be quite as pristine as those made at the start even if stampers are replaced on schedule.
And, as others noted, the quality of vinyl is also an issue. There is good quality vinyl available, but like any other business, some companies will put quality control second to cost factors.
A lacquer coated metal master is cut, which is electroplated to form a negative, which in turn is used to make a new all metal mother, which then is electroplated again to make the negative stamper plates.
Impurities in the plating chemicals, dust, or sloppy handling at any stage can cause noise in the stamped record.
Stampers can also be used past their prime. Stampers also do not typically fail instantaneously, so LPs made toward the end of the stamper's life will not be quite as pristine as those made at the start even if stampers are replaced on schedule.
And, as others noted, the quality of vinyl is also an issue. There is good quality vinyl available, but like any other business, some companies will put quality control second to cost factors.