I have a Miller 212. I'm using 0.030 wire with mild steel from my local steel place. This is the same steel I was using yesterday.
You will notice how I am getting black residue around the weld areas and when I turned up the gas pressure I get brown real close to the weld then black after that.
I am still using the same spool of wire and it looks clean.
This shot I am using 45 cfm gas pressure on the right and 25 cfm gas pressure on the left weld. I usually run lower cfm but when I had my machine in for the board problems the gent there said I needed to run more cfm. This is using the autoset feature on 1/8" steel.
This next picture is same heat setting with about 35 cfm gas.
I should mention that is does not sound the same when I am welding. It also does not look the same. The area around the puddle is doing some funky stuff as I well but I really have no idea how to explain it.