AN MD80 RETURNED TO THE GATE TWICE FOR RPTS OF A HOT ODOR. THE FIRST WAS CHKED BY MAINT AND FIRE RESCUE; NOTHING FOUND. THE SECOND OCCURRED IN AIR AND ON THE RETURN AGAIN NOTHING WAS DISCOVERED.

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WE DEPARTED OUR GATE AT ZZZ THE FIRST TIME AT XA50 BUT; DURING TAXI; BOTH THE FO AND MYSELF NOTICED AN ODOR BEST DESCRIBED AS A HOT GALLEY WITH FOOD INSIDE. FRANKLY; I DID NOT PAY MUCH MIND TO THIS AS THIS OFTEN OCCURS. VERY SOON THE FIRST FLT ATTENDANT CAME FORWARD TO INFORM US OF A HOT ODOR IN THE CABIN. A CHK OF THE FORWARD GALLEY OVEN REVEALED THAT IT WAS OFF AND COOL. NO SMOKE; FUMES; OR OBVIOUS PAX DISCOMFORT NOTED AT THIS TIME. I THEN REQUESTED THE FIRST FLT ATTENDANT TO QUERY THE AFT FLT ATTENDANTS ABOUT THE CONDITION OF THEIR GALLEYS. THE NEXT THING TO OCCUR WAS A SERIES OF CABIN CHIMES INDICATING A SMOKE DETECTOR IN A LAVATORY HAD ACTIVATED (I PURPOSELY CANCELED SELCALL AT THIS POINT AS ITS CHIME IS OFTEN CONFUSED WITH SMOKE DETECTOR ACTIVATION). THE FLT ATTENDANTS WERE ABLE TO DETERMINE THAT THE R AFT LAVATORY DETECTOR WAS THE CULPRIT AND RESET SAME. IT REMAINED QUIET. STILL NO SMOKE OR PAX/CREW DISTRESS; SO I ELECTED TO TAXI BACK TO THE GATE BUT HAD FIRE EQUIP FOLLOW US TO THE GATE. PAX WERE DEPLANED NORMALLY. FIREFIGHTERS INSPECTED THE ACFT VISUALLY AND WITH INFRA-RED CAMERA. NO EVIDENCE OF FIRE NOTED. ACFT THEN TURNED OVER TO OUR MAINT PERSONNEL. MAINT CONDUCTED AN INSPECTION OF THE ACFT BUT NO REAL DISCREPANCIES WERE FOUND. THEY DID; HOWEVER; INSPECT AND TIGHTEN SOME DUCTING AND REPLACED A FILTER 'SOCK.' WE NEXT DEPARTED THE GATE AT ABOUT XC30 AND EVERYTHING WENT NORMALLY UNTIL AFTER TKOF AT ABOUT 3000 FT MSL WHEN THE FO AND MYSELF HEARD MULTIPLE CABIN CALL CHIMES. IN STEPPED THE FIRST FLT ATTENDANT TO INFORM US THAT THERE WAS A HOT ODOR IN THE CABIN AND PAX WERE STARTING TO PANIC. AT NO TIME DID THE COCKPIT CREW NOTICE ANY SMOKE/ODOR. MY VISUAL CHK OF THE CABIN DID NOT INDICATE ANY SMOKE. WE WERE NOW LEVEL AT 9000 FT MSL IN THE VICINITY OF XXX. I NEXT INSTRUCTED THE FIRST FLT ATTENDANT TO DO A WALK-THROUGH OF THE CABIN AND RPT THE CONDITION. SHE DID SO; AND RPTED THE ODOR STILL PRESENT AND THAT PAX 'WERE VERY CONCERNED' AND 'I DO NOT FEEL COMFORTABLE WITH THIS SIT.' MY DECISION WAS TO REQUEST RETURN TO ZZZ ON ACCOUNT OF ODOR IN THE CABIN. WE DID SO UNEVENTFULLY; ALTHOUGH FIRE EQUIP MET US ON THE TXWY AND DID A VISUAL INSPECTION OF THE ACFT; BUT EVERYTHING APPEARED NORMAL. I DID NOT DECLARE AN EMER; FIRE EQUIP WAS REQUESTED BY ATC PERSONNEL. EXTERIOR INSPECTION REVEALED NO FIRE/SMOKE AND WE RETURNED TO THE GATE AND DEPLANED. CURIOUSLY; NEITHER THE FO NOR MYSELF NOTICED ANY ODOR; BUT SEVERAL PAX MADE COMMENTS TO ME THAT THEY INDEED HAD SMELLED SOMETHING AND STATED THEY WERE HAPPY WITH THE DECISION TO RETURN. ONE PAX DESCRIBED THE ODOR AS 'BURNING ELECTRICAL INSULATION AND I KNOW WHAT THAT IS.' ANOTHER THOUGHT THE ODOR HAD BEEN PRESENT IN THE CABIN WHEN THE ACFT DEPARTED MEXICO ON A PREVIOUS LEG (DIFFERENT CREW). DUE TO UNAVAILABILITY OF ANOTHER ACFT AND CREW DUTY ISSUES; THIS FLT WAS SUBSEQUENTLY CANCELED. ON REFLECTION ABOUT THESE INCIDENTS IT SEEMS THAT THIS ACFT; THE MD80; AT OUR AIRLINE AT LEAST HAS MORE THAN ITS SHARE OF CABIN SMOKE/FUME/ODOR PROBS. I DON'T KNOW IF THIS COULD BE MAINT OR DESIGN PROBS. CERTAINLY OUR ACFT HAVE HIGH UTILIZATION AND THE FLEET IS AGING. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED ON TAXI OUT THE FO AND MYSELF NOTED A HOT GALLEY LIKE SMELL BUT NOTHING ABNORMAL AS THE GALLEY IS LOCATED AFT OF THE COCKPIT. THE RPTR SAID THE GALLEY OVENS WERE RPTED COOL. THE RPTR STATED A LAVATORY SMOKE ALARM SOUNDED IN THE AFT LAVATORY AND WE RETURNED TO THE GATE. THE RPTR SAID THAT FIRE RESCUE CHKED THE CABIN FOR HOT SPOTS AND FOUND NONE AND MAINT REPLACED A WATER BAG. THE RPTR SAID AFTER TKOF BTWN 3000-9000 FT FLT ATTENDANTS AGAIN RPTED A HOT ODOR IN THE CABIN AND PAX WERE UPSET. THE RPTR SAID NEITHER THE FO NOR MYSELF SMELLED ANYTHING HINTING OF A HOT ODOR BUT WE NEVER LEFT THE COCKPIT. THE RPTR SAID WE RETURNED TO ZZZ WHERE THE AIRPLANE WAS TAKEN OTS. THE RPTR SAID THE CAUSE OF THE HOT ODOR; IF FOUND; WAS NEVER RPTED BY MAINT.