[rnln]

Milt,
Let me see if I understand this part right. You are saying that for better penetration, I don't have to have gas. I can use the current setup (weld with flux core wire, no gas). Ben probably meant to suggest me to use gas for the weld quality/look.
I had tried different thicknesses before. To do this, I usually start at the thicker piece first and stay at it longer then at the thinner piece. I also adjust the wire speed a little slower so I can stay longer withing flooding the weld.
Until now, my weld are always mixture. Sometimes I can have a very nice looking weld, but sometimes it look just ugly and I can't tell why. Maybe the power wasn't stable because someone was using something heavy such as AC or heater?
I will try to take some pictures and post.

jyl,
The reason why I don't want to dig deep into this myself because I don't see any crack nor anything wrong with my eyes. It was only from someone, who I can trust, said that he have seen this problem/noise in the past, and usually the problem was this weld. Instead of bring it in, I was thinking of trying to add some weld all around the edges to see if I am lucky (if welding these pieces is not that hard). If not, then I know for sure the problem is somewhere else.

Thank you all.