As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
TAXIING TO GATE, APU BLEED SOURCE SELECTED. RT PACK TURNED ON AND LITE SMOKE ENTERED CABIN. CONTRACT MTC. RAN APU FOR OVER AN HOUR WITH NO FURTHER FUMES/SMOKING. INSPECTED PACK BAY FOR ANY EVIDENCE OF HYDRAULIC LEAKS, NONE FOUND. UNABLE TO DUPLICATE PROBLEM.