Was there ever any pics taken of the bad weld or location of it that can be shared?I escalated to Ford customer service understanding the number of attempted fixes I'd had and the possible brevity of the problem. Ford brought in a CSM then a Ford field engineer took over the diagnositcs. Later an RSM got involved and a chassis enginèr at Ford corporate. In the diagnosis both the dealer and engineer confirmed independently it was a bad weld. The dealer played a big part in this too.
One thing I will say is if with every attempted fix the sound stays the same but comes up under different conditions ie originally for me it was on a right turn....then after a fix it would change to right and left turns but be inconsistent, then you very well might have this issue.