wire isnt wire. Farm migg'ers might not feel, hear, see the difference but a pro will.
Purity of metal, cleanliness of the spool. Age and how it was stored. Heck a welder buddy of mine was having issues with his mig at work, sputtering and popping here and there then it would be fine, then start back up... and all kinds of crap. Fought with settings, changed gas tanks, tips, spool tension, roller tension... nothing seemed to be working.
Then he though you know this is a lot like when someone changes the wire to a thinner gauge and doesn't change the feed tip on the torch. so when it started acting up again he shut the machine off and stripped out a few feet of wire. put it through a new tip and noticed it was way too loose. pulled another 20 feet of wire and tested the fit in the same tip, and it was fine.
Turned out the spool of wire was apart of a recalled group of spools from Lincoln for having inconsistent wire gauges.