I have 42k miles on a 2003 SE and recently noticed a strong coolant and humidity smell (perhaps coolant fumes?) inside the cabin. I had a similar problem with a 1994 Altima. I just can't believe this is now due also to a leak in the heater core so soon on a 03? Would this be the only cause? Recommendations? Just hate to apply a radiator stop leak product to the maxima.