In the past 8 years i have owned quite a few 4 th gen Maximas and 1st gen i30s..7 to be exact....Why do they all have a musty/mildew smell inside,i don't see any leaks inside, Can anybody give me an of where this problem could be coming from....Thanks.....BTW, I will never stop buying these cars regardless...

 

Probably from your vents. Take a can of Lysol or special deodorizer spray they have at auto stores. Roll down your windows and turn your fan on high. Then start spraying in those screened holes under your drivers side wiper blade. Fixed my musty smell. Ac mold I'm sure. Gets nasty in the evaporator box.
Edit: Make sure recirculate is OFF.
The directions on the can/Pure Air is the brand I use/ will tell you everything you need to know.
Make sure you have a while to air out your car and vents before you drive. It's pretty strong smelling itself.
Also, make sure your car is "sweating" properly when using your ac, because the drain hole for your evaporator could be clogged with twigs, ect.
Let me know if this helped you.

 

Wrong section.... but changing your cabin air filter will help.

 

completely wrong section. anyway, no cabin filter in the 4th gen. you'll figure something out