A DC9-30 IN CRUISE AT FL350 DECLARED AN EMER DUE TO ERRATIC PITCH TRIM INDICES MOVEMENT WITH NOISE IN TAIL COMPARTMENT CAUSED BY LOOSE INDICE CABLE.

Narrative

AT FL350; UPON LEVELOFF; WITH ACFT ON AUTOPLT; THE ACFT STARTED A CLB/DSCNT 200-500 FPM (INDICATED) ON THE IVSI. FO DISCONNECTED AUTOPLT AND HAND FLEW ACFT AND ALSO RETRIMMED ACFT. JUST AFTER HE RETRIMMED ACFT; I NOTICED THAT THE TRIM INDICATOR ON THE PEDESTAL WAS MOVING BOTH BACKWARD AND FORWARD APPROX 1/4 INCH. THIS CONTINUED THROUGHOUT THE FLT. ABOUT 1/2 WAY THROUGH THE FLT; FLT ATTENDANT WXXW CAME UP AND TOLD US THAT SHE HAD HEARD A KNOCKING NOISE AS WELL AS A VIBRATION ON DEP; CLBOUT AND AT CRUISE. FLT CTLS WERE NORMAL AND FELT NORMAL. I WENT BACK TO THE AFT PART OF THE CABIN; AND I TOO FELT THE VIBRATION AND ALSO HEARD A SLIGHT KNOCKING WHICH IS NOT NORMAL. DISCUSSED THAT WITH DISPATCH AND MAINT CTL; GAVE MAINT ALL THE INFO I HAD. THEY SAID IT MIGHT BE THE CABLE ATTACHED TO THE TRIM INDICATOR; SO WE PRESSED ON. NOT LONG AFTER; THE FLT ATTENDANT WXXW CAME UP TO THE FLT DECK AND INFORMED US THAT THE KNOCKING AND VIBRATION WAS GETTING STRONGER. THE TRIM WAS STARTING TO TRIM AGAIN WHILE THE FO WAS HAND FLYING THE ACFT. I MADE A CALL TO DISPATCH AND INFORMED THEM OF THE INFO JUST STATED; AND I DECIDED THAT I WAS GOING TO DECLARE AN EMER BECAUSE I WASN'T SURE WHAT WOULD HAPPEN WHEN WE START TO CONFIGURE THE ACFT FOR LNDG. AS WE STARTED CONFIGURING THE ACFT; WE NOTICED THAT AS FO TRIMMED THE ACFT AS FLAPS AND GEAR WERE EXTENDED THE TRIM INDICATOR WOULD MOVE TOWARDS THE NOSE DOWN POS. I ASKED FO IF HE FELT ANY NOSE DOWN PRESSURE; HE SAID 'NO.' (EXAMPLE: TRIMMED FLAPS 15 DEGS/GEAR DOWN TRIM WAS AT 5.8 -- TRIM WENT BACK 5.1.) FIRE EQUIP WAS STANDING BY; BUT WAS NOT NEEDED AFTER LNDG.