WE HAD THIS 2002 UNIT INSTALLED SEVERAL YEARS AGO AND WE HAD THEM PUT A RETURN AIR VENT OUTSIDE SO THAT WE COULD CHANGE THE FILTER(THE OLD UNIT WAS THAT WAY) LATELY I NOTICED MOLD ON THE INSIDE CLOSE TO WHERE THE FILTER GOES. iT'S ON THE SPINE FINS INSIDE- NOT THE SPINE FINS ON THE OTHER SIDE OF THE UNIT THAT YOU SEE FROM THE OUTSIDE. I'M NOT SURE IF I CAN CLEAN THESE OR NOT?