What was found
CLIMBING THROUGH FL180, THE CREW BEGAN TO NOTICE ODD ODOR IN THE COCKPIT AND THE CABIN, WITH THIN HAZE/SMOKE VISIBLE. THE CREW STARTED A DESCENT AND THE HAZE/SMOKE DISSIPATED. THE CREW TURNED BACK AND MADE AN UNSCHEDULED LANDING AT THE DEPARTURE AIRPORT. THE AIRCRAFT LANDED SAFELY. MAINTENANCE INVESTIGATED AND IT WAS FOUND THAT B-NUT ON SERVO TUBE ASSY ON THE Y-DUCT ON RIGHT PACK BAY WAS LOOSE AND LEAKING AND THE INSULATION WAS MELTED. INSPECTED THE PACK BAY AND SURROUNDING AREA, NO FURTHER DAMAGES WERE FOUND.