Dehumidifier ! My house was the same way , it was never wet in my basement , but it always had a "damp" smell . After a while , I broke down and bought a dehumidifier the smell went away . You more than likely have a drain or two in the floor , mine does , and that dampness comes up from there and through the concrete . You will be surprised at how much water the dehumidifier will remove from the air . I had to dump the water out every day because it would fill up once a day , but I have since hooked it up to a drain hose .