2001 Dodge Intrepid Smell inside car

For a couple of years I get a smell inside car when car is running. Does not smell like rotten eggs, cannot smell it outside the car or under the hood. Smells like a dead animal but usually is only when weather is cooler or cold. Could this be an exhaust leak. There is no noise like you would expect in this case. Did not have the smell all summer but now it is back.