Burned water out of pot...popping sound a month later?
If you heated the metal to the point where you get rainbow colors on the surface after cooling, you'll likely have tempered and nontempered  areas on the pan bottom. These areas 1) have different coefficients of thermal expansion and 2) can move around with subsequent heating. The pops are likely the bottom of your pan buckling as it adjusts to different parts of itself expanding/contracting at different rates. I wouldn't worry about it.