What was found
(CAN) A PAX REPORTED SMOKE IN CABIN. THE EVENT WAS NOTED DURING CLIMB FROM AT APPROX 12K FEET. SUSPECTED THE ISSUE TO BE OIL MIST. DECLARED AN EMER & RETURNED TO DEPARTURE AIRPORT. THE ACFT LANDED & TAXIED WITHOUT ANY ISSUES. TROUBLESHOOTING REVEALED THAT IT APPEARS TO BE WORSE WHEN NR 2 ENG BLEED SELECTED. A TECHNICIAN IS ON SITE. GND RUNS OF 5 MINUTE WERE PERFORMED & UNABLE TO REPRODUCE THE ISSUE. MFG PROPOSED TO PERFORM A COAT ANALYSIS. MFG WILL INVESTIGATE TO ESTABLISH ROOT CAUSE & PROVIDE INFORMATION THROUGH SUBSEQUENT SERVICE DIFFICULTY REVIEW MEETING & SUPPORTING DOCUMENTS OR OTHER AGREED UPON COMMUNICATIONS.