I'm using a PP256. I have no idea what kind of aluminum I have. It's just some scrap 0.50" sheet from work. I don't think the popping is from hitting the weld pool cause it happens right after I have sharpened the tungsten before I've even dipped the filler rod. I am hitting the puddle quite a bit though as I weld. maybe the contamination is higher up than just the point. I also tried turning the argon up to about 9cfm. Had it at 7cfm but I haven;t tried to bring it down at all. I'm using a 1.6mm 2%Thoriated with a 5 cup. I'm going to grab some more scrap from work and practice some more this week. I'm also going to pick up a virgin SS brush to clean before I weld.