What was found
AIR CONDITIONER COMPRESSOR STARTED TO MAKE A LOUD NOISE WITH THE SMELL OF RUBBER IN THE COCKPIT, WHILE ON LANDING. TUNED THE AIR CONDITIONER OFF, THE SMELL AND NOISE STOPPED. AFTER LANDING, CALLED MAINTENANCE, FILLED OUT THE MEL DEFERRAL, AND PUT THE AIRCRAFT BACK IN SERVICE. DURING THE MAINTENANCE INSPECTION, THE EARLIER LOUD NOISE AND SMELL COULD NOT BE DUPLICATED.