FLT CREW OF MD80 EXPERIENCE MISALIGNED HEADING INFO ON FMS DISPLAY. SUSPECT PAX OPERATED ELECTRONIC DEVICES.

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DURING TKOF ROLL; RECEIVED 'HEADING' ANNUNCIATIONS ON FMS FLT MODE ANNUNCIATOR PANEL (FMA) WITH ABOUT A 10 DEG HEADING SPLIT. WE ELECTED TO CONTINUE THE TKOF RATHER THAN ABORT AT HIGH SPD AND NOTED THAT THE FO'S HEADING MATCHED THE RWY HEADING MORE CLOSELY. THIS PROB OCCURRED INTERMITTENTLY FOR THE NEXT 5 MINS WITH AN 8-10 DEG HDG SPLIT AND THE HEADING CHANNEL (ROLL WINDOW) BLANKING OUT ON THE FMA. (THE AUTOPLT COULD NOT ENGAGE IN THIS CONDITION.) I SUSPECTED ELECTRONIC INTERFERENCE AND DIRECTED THE FLT ATTENDANTS TO SWEEP THE CABIN AND CHK FOR USE OF PERSONAL ELECTRONIC DEVICES WHILE THE FO MADE AN ANNOUNCEMENT TO REQUEST PAX DOUBLE-CHK THAT DEVICES WERE TURNED OFF. FLT ATTENDANTS ALSO HAD PAX CHK DEVICES IN CARRY-ON LUGGAGE. SHORTLY AFTER DIRECTING THESE CHKS; THE PROB CLRED UP; CAPT AND FO HEADING REFS AGREED WITH EACH OTHER AND THE WHISKEY COMPASS. THERE WERE NO PROBS FOR THE REMAINDER OF THE FLT; INCLUDING AFTER WE ALLOWED LAPTOP COMPUTERS TO BE USED. FOR ADDITIONAL REF; THIS WAS AN AHRS ACFT (DID NOT HAVE IRS-BASED HEADING SYS). ALSO; ALTHOUGH NO PAX ADMITTED HAVING ANY DEVICES ON; A FLT ATTENDANT WHO WAS SEATED IN THE BACK LATER MENTIONED THAT SHE HEARD AT LEAST 1 CELL PHONE RINGING ON TKOF ROLL. (THE FLT ATTENDANTS HAD MADE THE STANDARD PREFLT PA TO TURN DEVICES OFF.) WE HAVE AN ABNORMAL PROC IN OUR MANUALS FOR HEADING ERRORS; BUT IT WASN'T EFFECTIVE DURING THIS EVENT. SINCE IT WAS VFR; THIS DIDN'T SERIOUSLY DEGRADE SAFETY; ALTHOUGH IT WAS A DISTRACTING EVENT IN A BUSY ATC ENVIRONMENT. HAD THIS HAPPENED DURING AN APCH IN IMC CONDITIONS; IT WOULD HAVE BEEN MORE SERIOUS. PERHAPS THE TRAVELING PUBLIC NEEDS TO BE MADE MORE AWARE THAT PED USE DURING FLT IS A SERIOUS CONCERN.