FLC OF A CPR JET TOOK OFF EVEN THOUGH THE EMER LOCATOR XMITTER (ELT) WAS GOING OFF DURING TAXI FOR TKOF.

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WHILE TAXIING FOR DEP ON RWY 23 AT MMU; THE GND CTLR CALLED US TO SEE IF WE WERE RECEIVING AN ELT ON 121.5. I TUNED THE #2 COM AND RPTED AFFIRMATIVE. THE GND CTLR THEN ADVISED US THAT AN 'FAA' MAN AT OR NEAR THE FBO HEARD IT ALSO; AND SAID IT GOT WEAK AS WE TAXIED AWAY; INDICATING THAT IT WAS OURS. I ADVISED GND THAT I WOULD CYCLE AND RESET OUR ELT; AND ASKED HIM TO RPT ANY CHANGES IN THE SIGNAL WHICH I DID. HE RPTED NO CHANGE; BUT A UTILITY VEHICLE PARKED NEXT TO US IN THE RUNUP BLOCK SAID THAT THE ELT SIGNAL ON HIS RADIO WAS BLEEDING OVER ONTO GND CTL. HAVING NO IMMEDIATE WAY TO VERIFY THAT IT WAS IN FACT OUR ELT; AND BEING IFR RELEASED TO OUR DEST; AND HOME BASE; PHL; WE TOOK OFF. I WAS STILL MONITORING 121.5 AT THAT TIME; AND AS WE BEGAN OUR TKOF ROLL; THE ELT SIGNAL STOPPED; WHICH; WHEN I MADE MY NEXT CALL TO MMU LCL CTL; HE CONFIRMED; AND ENTERED IN THE TWR LOG (WHICH I LEARNED THE FOLLOWING DAY). ENRTE TO PHL THE ELT BEGAN XMITTING AGAIN; WHICH WE ADVISED PHL LCL CTL OF. WE DEPLANED OUR 2 PAX AFTER LNDG; AND WERE IMMEDIATELY TUGGED INTO OUR HANGAR. ENRTE TO PHL I HAD CONTACTED OUR MECH ON OUR FLITEFONE; AND RECEIVED INSTRUCTIONS ON HOW TO GAIN ACCESS TO THE ELT; WHICH I DID AS SOON AS WE WERE IN THE HANGAR. BY THE TIME OUR MECH ARRIVED FROM HOME; WE HAD DISCONNECTED THE ELT FROM BOTH OF ITS ANTENNAS; AND REMOVED THE PLUG THAT CONNECTS IT TO THE ON/ARM/RESET SWITCHES IN THE COCKPIT. APPARENTLY IT HAD BEEN OUR ELT SINCE THERE WAS A RED LIGHT EMITTING DIODE ON IN THE ELT CASE; AND MONITORING OF 121.5 AFTER DISCONNECTING THE PLUG REVEALED NO ELT SIGNAL. OUR MECH IS TROUBLE-SHOOTING THE SYS TO DETERMINE WHAT ACTIVATED THE ELT.