What was found
AFTER APU STARTUP AND SWITCHING FROM THE ENGINE BLEEDS TO THE APU BLEEDS A BURNING SMOKE SMELL WAS NOTED, BUT NO VISIBLE SMOKE IN THE COCKPIT NOR CABIN. AFTER LANDING A FAINT HINT AND TASTE OF SMOKE WAS NOTED IN THE AFT CABIN NEAR THE LAVATORY. THE BURNING SMELL AND TASTE IN THE CABIN WAS OF AN OIL NATURE. THE PASSENGERS MADE A COMMENT OF A SMELL WHEN THEY DEPLANED. ALL CREW MEMBERS HAVE A MILD HEADACHE. CORRECTIVE ACTION: REMOVED COALESCER SOCKS P/N: 180849-28 AND REPLACED WITH CUSTOMER SUPPLIED NEW UNITS P/N: 180849-28 IAW CL-650 AMM, 21-51-13-000-801 AND COMPLETED ECS BURNOFF PROCEDURES. LEAK AND OPERATIONAL TESTS ARE SATISFACTORY AT THIS TIME.