Scratch your finger nail along the barrel or any chamber surface. If it makes noise, then it is not smooth enough. Small ridges from machining the barrel can wear down your original Glock slide.
Do polish the barrel to a mirror shine. Run your nail and it should have no noise.
Then I lube it with Frog Lube and mine worked beautifully ever since. Mfgr don't usually polish the barrels (takes time and costs money).