What was found
AIRCRAFT WAS GROUNDED, AIRCRAFT REPEAT EVENT. LOUD THUMP HEARD FROM NOSE GEAR COMPARTMENT RIGHT AFTER TAKEOFF AND ANOTHER LARGE THUMP AND SOUND ABOUT A MINUTE LATER. THEN WHEN WE LOWERED GEAR, THE LGCIU 2 FAILED. DECESION MADE TO RETURN TO DFW AIRCRAFT LANDED WIHTOUT INCIDENT. DURING INSPECTION OF AIRCRAFT FOR THUMPING NOISE, FOUND LEFT HAND PACK LNLET PLENUM BOOT DAMAGED. MAINTENANCE REPLACED RAM AIR EXHAUST BOOT IAW AMM 21-61-52.