What was found
ATB - STRONG SMELL IN COCKPIT AFTER T/O. RAN LEFT AND RIGHT ENGS & PRESSURIZED A/C WITH BLEED AIR FROM ENGS. ALSO WITH APU BLEED & NO ODORS NOTED. INSP LT & RT A/C PACKS INLET PRIM & SEC HEAT EXCHANGERS INSP PNLS, ALL OK. INSPECTED BEHIND C/B PNLS IN C/P, E&E & ALL OK. UPON FURTHER INSP, FOUND CLEANING CREW LEFT SOILED CLEANING RAG CAUSED ODOR. AIRED OUT A/C OK FOR SERVICE.