What was found
JUST AS AIRCRAFT LEVELED OFF AT FL220, A STRONG ELECTRICAL SMELL AND LIGHT SMOKE APPEARED IN THE CABIN. BOTH THE FORWARD AND AFT LAVATORY SMOKE DETECTORS ACTIVATED. NO MENTION OF COM COMPLIANCE OR PACK CONFIGURATION. CREW DECLARED AN EMERGENCY AND RETURNED TO AN OVERWEIGHT LANDING AT DTW. MAINTENANCE DID NOT FIND ANY OBVIOUS FAULT OR ANY EVIDENCE OF FIRE. POSSIBLE INGESTION OF INSULATION BY PACK COOLING FAN MAY HAVE CAUSED BURNING SMELL. MAINTENANCE CLEANED THE HEAT EXCHANGER AND REPLACED THE WATER SEPARATORS. AIRCRAFT RETURNED TO SERVICE.