B737-800 CREW HAD AN UNCOMMANDED RUDDER MOVEMENT ON TKOF; AND INFLT; DECLARED EMER AND RETURNED TO ARPT AND LANDED.

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ACFT SYSTEM FAILURES; FLT CTLS. FO FLYING; ON THE TKOF ROLL WE FELT THE NOSE PULL TO THE R AT APPROX 100 KTS. HE CORRECTED TO THE CTRLINE WITHOUT PROB; BUT WE FELT THE SAME OCCUR DURING ROTATION AND AGAIN; TO A LESSER EXTENT; AT APPROX 1000 FT AGL. FOLLOWING CLEANUP; THE ACFT SEEMED TO BE NORMAL. HOWEVER; WITH MY CONCERN FOR POTENTIAL B737 RUDDER PROBS; I ASKED THE FA IF ANY OF THEM NOTICED ANYTHING UNUSUAL ON TKOF. WITHOUT MY PROMPTING; THEY EACH DESCRIBED WHAT WE HAD FELT IN THE COCKPIT; MUCH MORE SIGNIFICANT IN THE REAR OF THE JET; AND I FELT I NEEDED TO GET HOLD OF DISPATCH AND MAINT CTL. WE ALL QUICKLY AGREED THAT WE SHOULD RETURN TO THE ARPT. WE NOTIFIED ATC; DECLARED AN EMER; AND RETURNED TO LAND SIDESTEPPING TO PARALLEL RWY UNEVENTFULLY. CTR; TRACON; AND TWR/GND WERE ALL QUITE HELPFUL AND EXPEDITIOUS. WITH THE HISTORY OF B737 RUDDER ISSUES ON OLDER MODELS; I FELT IT WAS THE SAFEST COURSE OF ACTION. SUPPLEMENTAL INFO FROM ACN 632454: IMMEDIATELY BEFORE AND AFTER ROTATION THERE WAS CLEARLY A RUDDER JERK THAT LUNGED THE ACFT SLIGHTLY THEN CORRECTED QUICKLY. CALLBACK CONVERSATION WITH RPTR ACN 632443 REVEALED THE FOLLOWING INFO: THE CAPT FILED AN ACR RPT. THIS ALLOWED THE FLT RECORDER TO BE READ OUT. THE FLT RECORDER READOUT WAS INCONCLUSIVE. IT SHOWED THE RUDDER PEDAL MOVEMENT THE FO PUT IN TO CORRECT TO THE CTRLINE OF THE RWY. THE CAPT TALKED TO THE ASSISTANT CHIEF PLT FOR THE B737; TO BRIEF HIM ON ALL THE DETAILS. THE RPTR DOES NOT KNOW WHAT WAS FOUND; OR WHAT MAINT ACTION WAS TAKEN.