Mold growing on inside of new windows

Looking at your pic and arrows, it looks like the bottom sash does not fit well. If all the factory weather seals are in place, not damaged or worn, I think they may be poor quality. That is rare since most windows in the last 10 years or so are normally fairly tight. The area that really concerns me are the sides where you show the arrow. This area usually depends on a snug mechanical fit, not weather stripping to seal the unit. Does this lower unit seem loose? Leaking at the joint of the two sashes is common and can be fixed with new seals most of the time, but the sides do not. Also, some windows need to be locked for the sash to sash seal to fully engage.

Caulking is not a good way to seal these kind of leaks if you ever want to open them again!

Maybe you can more fully describe the areas in question and the fit of the windows.

Single glazing with storm windows absorbs sound reasonably well, I would not expect a huge decrease in sound level with triple glazing, but certainly not an increase. Single glazing alone is another story, it's sound absorption is terrible.

The increased sound is certainly due to the frames and adjacent construction. While there is often a correlation between thermal loss and sound transmission, sound is much trickier to manage well. It is sometimes counter intuitive. The construction joints must be carefully detailed. The general concept is to avoid any solid connection between inner and outer surfaces. Any connections should be via resilient, absorbent materials. Typically, you want to fill any voids with sound insulation, though in some cases this has been worse than a simple air gap.

Also consider exterior sound attenuators. Walls, fences, trellises, large shrubs, trees, berms all will help attenuate sound, but when you consider cost vs. benefits, such measures need to be carefully considered.