B767 FLT CREW REPORTS UNUSUAL NOISE FROM NLG AFTER TKOF AND ELECTS TO DECLARE AN EMERGENCY AND RETURN FOR UNEVENTFUL LANDING.

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AFTER A NORMAL PREFLT AND TAXI-OUT; WE COMMENCED A NORMAL TKOF. IMMEDIATELY UPON LNDG GEAR RETRACTION; WE NOTICED A LOUD NOISE AND VERY STRONG VIBRATION FROM THE NOSE LNDG GEAR AREA. THE VIBRATION WAS SIMILAR TO WHEEL SPIN DOWN BUT WAS FAILING TO DECREASE IN FREQ AND VOLUME. THE CAPT (PNF) IMMEDIATELY SELECTED GEAR HANDLE DOWN. THE GEAR EXTENDED AND THE NOISE AND VIBRATION CEASED. THE LNDG GEAR INDICATED 'DOWN AND LOCKED' WITH 3 GREEN LIGHTS. THE LNDG GEAR DOOR IN-TRANSIT LIGHT WAS NOT ILLUMINATED. AN EMER WAS DECLARED WITH TWR AND THE ACFT CONTINUED STRAIGHT OUT FROM THE RWY. WE CLBED TO 5000 FT AND BEGAN CIRCLING VECTORS WITH APCH. THE FLT ATTENDANT WAS CONTACTED THROUGH INTERPHONE AND ASKED THAT ALL FLT ATTENDANTS REMAIN IN THEIR JUMP SEATS. THE CAPT CONTACTED BOTH DISPATCH AND MAINT THROUGH A PHONE PATCH. AFTER DISCUSSING ALL POSSIBLE CAUSES AND OUTCOMES OF THE SITUATION; THE CREW DECIDED TO RETURN TO ZZZ AND PREPARE THE CABIN FOR EVAC. THE FLT ATTENDANT WAS NOTIFIED TO COME TO THE COCKPIT IN WHICH THE CAPT EXPLAINED THE SITUATION AND THE DECISION TO RETURN TO THE ARPT WITH A FULL CABIN PREPARATION FOR EVAC. ALL PERTINENT INFO SUCH AS LNDG CONDITIONS; SPECIAL NEEDS PAX AND THE BRACE SIGNAL WERE DISCUSSED. THROUGH BOTH ATC AND DISPATCH; ARRANGEMENTS FOR A LOW-LEVEL FLY-BY AND RETURN TO ARPT WERE MADE. AFTER COMPLETING THE PREPARATION FOR EVAC AND PLANNING AND BRIEFING THE LOW-LEVEL APCH/INSPECTION AND THE SUBSEQUENT LNDG; THE CREW COMPLETED THE APCH AND FINAL DSCNT CHKLIST AND RETURNED TO THE FIELD. A LOW-LEVEL FLY-BY WAS PERFORMED AT 500 FT OVER THE CTRLINE OF RWY XX FOR TWR INSPECTION. NO ABNORMALITIES WERE NOTED FROM THE TWR. A LAST CHK OF EMER EQUIP STATUS WAS MADE AND THE ACFT RETURNED FOR LNDG.