What was found
FLIGHT ATTENDANTS AND PASSENGERS REPORTED SMOKE ODOR IN CABIN DURING TAKEOFF. FLIGHT RETURNED TO DTW, LANDING UNEVENTFULLY. PILOTS NOTED NO ODOR IN FLIGHT DECK, APU NOT RUNNING. FLIGHT ATTENDANTS REPORTED ODOR WAS NOT FROM DEICING FLUID. CORRECTED BY BORESCOPING BOTH ENGINES (L/P 3640504) AND CHECKING APU BLEED AIR, NO WETTING NOTED. MAINTENANCE UNABLE TO DUPLICATE SMOKE ODOR. NO PART CHANGES DIRECTLY ASSOCIATED WITH FUME EVENT.