1995 Ford F350 V8 Four Wheel Drive Automatic 140000 miles

I have 1995 fORD f350 1 TON ,MY 4X4 HUBS ARE MAKING LOUD ENGAGING NOISE WHEN IN 2 WHEEEL DRIVE,MY MECHANIC SAID THERE IS ALOT OF METAL SHAVING IN THE HUB ASSEMBLY,I JUST BOUGHT THIS TRUCK USED ,NEVER USED THE 4 WHEEEL DRIVE UNIT YET,I DID HAVE THE TRANNY REPLACED ,THE MECHANIC AT AAmco said after tranny was done he took for test ride heard gears engaging also in 2 wheel drive ,tried to determine from were coulnd find ,this doesnt happen all the time ,when Aamco installed tranny is it possible they didint alain something correctly i didnt have problem until then.