Has it been especially rainy and humid where you are lately? Unless you have some moisture inside your car, it's probably just from high humidity. If you turn on your AC (regardless of what temp you use) while driving around, that will keep the air in the vehicle dry and prevent the fogging. I would also recommend checking in your spare tire well for water - I hear some folks have had some leaking problems around that area, but I forget exactly what the fix is. You may want to try a search for it...

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'08 335i Coupe - Barbera Red / Saddle Leather / Light Poplar Wood / 6spd Manual
Options: Sport, Premium, Cold Weather, Comfort Access, Active Steering (awesome!), Power Rear Shade, IPod Adapter, Navigation w/IDrive
Mods: M6 Wheels, Split Armrest, M-Steering Wheel, Euro Light Switch w/Rear Fog Lights, Short Shift Knob w/Matching E-Brake Handle, Clear Reflectors, CDV, Clear Bra

Retired:'04 X5 4.4i