1997 ford f150 4.6 engine rattle. Automatic 2wd?

have a f150 has a rattle under load or accelerating only does it when moving will not do it when rev it up setting still. Have changed the plugs and it still is doing it anyone else have this problem and know what it i?

Read more: 1997 ford f150 4.6 engine rattle. Automatic 2wd?