MD80 CREW HEARS LOUD NOISE AFTER GEAR RETRACTION. AFTER TROUBLESHOOTING THEY DECLARE AN EMER AND RETURN TO DEP ARPT.

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THE FLT CREW ARRIVED AT THE ACFT ON TIME AND PAX BOARDING COMMENCED SHORTLY THEREAFTER. ALL CHKLISTS WERE COMPLETED QUICKLY AND EFFICIENTLY AND FLT TOOK OFF 21 MINS AFTER CLOSING THE MAIN ENTRY DOOR; FROM RWY 18L. TKOF WAS PERFORMED BY THE FO. AS THE CAPT RAISED THE LNDG GEAR HANDLE; A LOUD NOISE AND VIBRATION WAS HEARD AND FELT COMING FROM THE NOSE GEAR AREA. OUR FIRST SUSPICIONS WERE THAT THE NOSEWHEEL WAS OUT OF BAL AND IT WAS VIBRATING EXCESSIVELY; BUT SINCE THE NOISE/VIBRATION CONTINUED; IT WAS APPARENT THIS WAS NOT THE SOURCE OF THE PROB. THE ACFT WAS ACCELERATED TO 200 KIAS WITH THE SLATS EXTENDED AND WE LEVELED OFF AT 4000 FT HDG S. THE CAPT LOWERED THE LNDG GEAR AND THE GEAR CAME DOWN AND LOCKED INTO POS NORMALLY WITH NO ABNORMAL INDICATIONS; HOWEVER; IT WAS NOTICED BY BOTH PLTS THAT WITH THE GEAR DOWN; THE NOISE LEVEL WAS MUCH LOUDER THAN USUAL. WE CONTACTED ATC AND REQUESTED RADAR VECTORING TO REMAIN NEAR THE ARPT. WE THEN LOWERED THE FLAPS TO 11 DEGS TO AID IN MANEUVERING AND TO IMPROVE DECK ANGLE FOR IMPROVED OUTSIDE VIEWING/CLRING. THE CAPT THEN RAISED THE GEAR HANDLE A SECOND TIME AND THE GEAR CAME UP NORMALLY WITH NO ABNORMAL INDICATIONS. AFTER GEAR RETRACTION; THERE WAS NO RED OR GREEN OR AMBER GEAR DOOR LIGHTS OBSERVED. WITH THE LNDG GEAR IN THE UP/RETRACTED POS THE LOUD NOISE AND VIBRATION BEGAN AGAIN. BOTH PLTS SUSPECTED THE PROB WAS NOT ASSOCIATED WITH THE LNDG GEAR ITSELF; BUT WITH THE SEQUENCING OF THE NOSE GEAR DOORS. THE FO TURNED ON THE AUTOPLT AND AUTOTHROTTLE AND FLEW THE ACFT AT 4000 FT WHILE THE CAPT REFERRED TO THE QRH. NO CHKLIST SPECIFICALLY REFED A 'SUSPECTED GEAR DOOR OPEN-NON ALERTED' CONDITION. THE CAPT REFED PAGE 4 LAND IN THE QRH. AFTER REFERRING TO THE QRH; THE CAPT CONTACTED MAINT. AFTER CONFERRING WITH THE TECHNICIAN; THE CAPT WAS CONFIDENT THE PROB WAS ONE OR BOTH FORWARD NOSE GEAR DOORS WERE STILL OPEN WHEN THE LNDG GEAR WAS UP. THE CONVERSATION WITH MAINT WAS DISCUSSED WITH THE FO. SINCE WE COULD NOT CONTINUE IN THIS CONDITION (HIGH FUEL BURN; EXCESSIVE NOISE/VIBRATION; POSSIBLE SEPARATION OF THE GEAR DOOR/DOORS) AND AN OVERWT LNDG WAS GOING TO BE REQUIRED; THE GEAR HANDLE WAS RAISED AND LOWERED ONE LAST TIME MONITORING ALL SYS. THE CAPT CONTACTED THE CABIN CREW WITH ONLY 2 CHIMES AND EXPLAINED THE SITUATION AND ASKED IF THERE WAS ANYTHING ABNORMAL IN THE CABIN. THE CABIN CREW RPTED EVERYTHING WAS PEACEFUL AND THE ACFT APPEARED NORMAL. THE CABIN CREW WERE ADVISED WE INTENDED TO MAKE A NORMAL LNDG AND WOULD STOP ON THE RWY FOR SOME INSPECTIONS AND TO BE AWARE OF EMER VEHICLES OUTSIDE THEIR ACFT AND NOT TO BE CONCERNED; THE ACFT WAS IN GOOD/STABLE CONDITION. A PA WAS THEN MADE TO THE PAX ADVISING THEM OF OUR INTENT TO RETURN. THE ACFT WAS IN EXCELLENT CONDITION (EXCEPT FOR THE NOSE GEAR DOOR OPEN AND SUBSEQUENT NOISE AND VIBRATION); THE LNDG GEAR WAS PROPERLY IN THE DOWN POS AND WE WOULD BE MAKING A NORMAL LNDG IN ABOUT 10 MINS. THE PAX WERE ALSO ADVISED TO REMAIN SEATED AND CALM AND NOT TO BE CONCERNED ABOUT ANY EMER VEHICLES OUTSIDE OF THE ACFT; THE WOULD BE MAKING ROUTINE INSPECTIONS. THE 'PREPARE FOR LNDG' PA WAS GIVEN AT THIS TIME. ATC WAS ADVISED OF OUR INTENT TO LAND ON AND WE DECLARED AN EMER AND ADVISED THE TWR WE WOULD BE STOPPING ON THE RWY AND REMAIN THERE UNTIL THE FIRE CHIEF AND ACR MAINT INSPECTED THE CONDITION OF THE ACFT. WITH ALL GEAR LOCKED DOWN INTO THE LNDG POS; ALL WARNING LIGHTS OUT AND THE ACFT CONFIGURED FOR LNDG; THE CAPT ASSUMED THE 'FIRST PLT' POS AND CTL OF THE ACFT FOR THE 'OVERWT LNDG' AT 138000 LBS; FLAPS 40 DEGS; AUTO BRAKES OFF. ALL CHKLISTS WERE ACCOMPLISHED IN A TIMELY MANNER. CONDITIONS FOR LNDG WERE CLR; LIGHT WINDS OUT OF THE N. LNDG OCCURRED AT XA45L. THE ACFT MADE A NORMAL LNDG AND WAS BROUGHT TO A STOP ON CTRLINE OF RWY AT ABOUT 1/2 WAY DOWN THE RWY. THE PAX AND CABIN CREW WERE ADVISED VIA A PA THAT WE WERE 'FINE' AND TO REMAIN SEATED. THE FIRE CHIEF AND SUPPORT EQUIP ARRIVED WITHIN 3-5 MINS AND ADVISED THE CAPT THAT THE ACFT LOOKED NORMAL. WECONTACTED THE TWR AND REQUESTED THEY CONTACT OPS TO REQUEST MAINT ASSISTANCE. THE TWR SAID THEY ALREADY WERE IN CONTACT WITH OPS. MAINT WAS CONTACTED TO ADVISE THEM WE WERE ON THE GND AND AWAITING THEIR INSPECTION FOR TOWING OR TAXI TO A GATE. THE 'AFTER LNDG CHKLIST' WAS COMPLETED. WE CONTACTED MAINT A SECOND TIME TO INQUIRE ABOUT THE STATUS OF THEIR PERSONNEL AND EXPECTED ETA. WE WERE ADVISED 'THEY ARE ON THE WAY.' MAINT ARRIVED AT THE ACFT AT XB09L. IT TOOK 24 MINS FOR MAINT TO GET TO THE ACFT! WHEN MAINT FINALLY ARRIVED AT THE ACFT; THEY ADVISED THE CAPT THAT THE R FORWARD NOSE GEAR DOOR WAS HANGING OPEN. WE HAD THE LNDG GEAR 'PINNED' AND TAXIED TO THE GATE UNEVENTFULLY. GATE PERSONNEL WERE READY FOR OUR ARR AND THE ACFT WAS DEPLANED QUICKLY. THE CAPT AND FO COMPLETED ALL CHKLISTS AND LOGBOOK ENTRIES AND WENT TO INSPECT THE NOSE GEAR DOORS. MAINT PERSONNEL EXPLAINED THAT THE R FORWARD NOSE GEAR DOOR WAS 'OUT OF RIG' WHICH CAUSED THE DOOR DURING GEAR RETRACTION NOT TO BE RAISED FULLY; THEREFORE; IT NEVER GOT TO THE POINT WHERE IT WAS ABLE TO LOCK UP IN THE CLOSED POS. ALL CREW THEN PROCEEDED TO THE NEW ACFT AT GATE AND FLT CONTINUED UNEVENTFULLY. ALL CREW PERFORMED ADMIRABLY AND ONLY 1 PAX COMPLAINED ABOUT BEING 'INCONVENIENCED.'