A B737-300 ON APCH AT 7000 FT EXPERIENCED RUDDER KICK AND VIBRATIONS. DECLARED EMER; MADE 2 GARS THEN LANDED. CAUSE UNKNOWN.

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ON L BASE VISUAL FOR RWY 28R; ZZZ; SPD 200 KTS FLAPS 2 DEGS; FELT A KICK IN R RUDDER THEN A VIBRATION OF LONGER DURATION IN RUDDERS (SIMILAR IN SOUND AND FREQ TO STICK SHAKER EXCEPT RUDDERS WERE VIBRATING). INITIATED GAR; NOTIFIED TWR OF POTENTIAL CTL PROB; DECLARED EMER; REQUESTED EQUIP; PROCEEDED TO AN AREA AWAY FROM ARPT WHERE WE COULD TROUBLE-SHOOT AND DO CHKLISTS. AUTOPLT AND AUTOTHROTTLE HAD ALREADY BEEN DISCONNECTED LONG BEFORE THE VISUAL APCH BEGAN. TURNED YAW DAMPER OFF; VIBRATION CONTINUED. ACFT CTL WAS SLUGGISH; UNPREDICTABLE. CONTACTED MAINT THRU DISPATCH. PERFORMED RUDDER PEDAL OSCILLATION AND AIRFRAME VIBRATION CHKLIST. ONCE B PUMPS WERE OFF; VIBRATION STOPPED. VIBRATION BEGAN AGAIN ON FINAL (B PUMPS ON PER CHKLIST; SPD 180 KTS; FLAP 15 DEGS.) WENT AROUND AGAIN; CONTINUED INTERMITTENT VIBRATION; CONSULTED MAINT CTL (NO NEW INSTRUCTIONS). ACFT CTL SEEMED MORE DIFFICULT; OPTED TO TURN BREAKERS OFF; LEAVE THEM OFF. CABIN HAD ALREADY BEEN PREPPED VIA INTERPHONE; PA TO PAX; CONFIGURED ACFT FOR FLAPS 15 DEG LNDG USING ALTERNATE FLAP OP CHKLIST. VIBRATION DID NOT RECUR. BRACE SIGNAL GIVEN AT 1000 FT. NORMAL TOUCHDOWN AND REVERSE/BRAKE OP. REMAIN SEATED COMMAND GIVEN ON ROLLOUT; TURNOFF AT TXWY F. EMER EQUIP CREW VERIFIED ACFT CONDITION APPEARED NORMAL. ACFT TAXIED TO GATE WHERE PAX DEPLANED NORMALLY.