Had the car been through a rain or car wash recently?
If there were no other sources of moisture inside the vehicle, I would suspect that your A/C evaporator/heater core chamber isn't draining properly. However, I think if that were the case you would have experienced some "musty" odors from your vents prior to now.
Hatch Nation #90
'12 SE Sport 5Dr |╠╬╝|Sterling Grey Metallic|203a|Moonroof|17" Paint/Mach Whls|K&N 57S-4000|FFE RMM|Steeda STB, RSB|JBR bushings
'01 ZX3|╠╬╝|Pitch Black|Prem. pkg.|Moonroof|SVT Snorkel|SVT Springs|S2 Dampers|Steeda STS|Magnaflow exh.