What was found
AIRCRAFT WAS GROUNDED: DURING ENG 2 START IN CLT WE HEARD A THUMP AND FELT A VIBRATIONIN THE RUDDER PEDALS. WE CHECKED THE CONTROLS AND DID NOT EXPERIENCE ANY THING ELSE OUT OF THE ORDINARY DURING TAXI OUT. AFTER DEPARTURE THE FO STATED THAT HE HEARD A BANG. HEARD IT THE NEXT TIME AS WELL. WERE IN AN EMPTY AIRCRAFT AND IT ALMOST SOUNDED LIKE SOMEBODY WAS IN THE GALLEY. FOUND NOTHING OUT OF THE ORDINARY WHEN I WENT BACK TO THE GALLEY. EVENTUALLY WE ISOLATED THE SOUND AND VIBRATION TO COMING FROM DIRECTLY BELOW THE FIRST OFFICER'S LEFT FOOT. INFORMED DISPATCH, EVENTUALLY DIRECTED US TO DIVERT TO DFW. MAINTENANCE ACCOMPLISHED PROCESS FOR THE IDENTIFICATION OF VIBRATION OR NOISE PER TSM 05-50-00 ALL CHECK NORMAL, TAXI A/C NO NOISE NOTE.