Really loud rattling coming from the front of my truck

[Maengelito]

rattling can happen at certain rpm's as well, i guess certain frequencies from different engine rpms would work the heat shield causing it to rattle. i think the cat's heat shield on my sti rattles ever so slightly at around 3400 rpm. its sometimes audible under acceleration but its usually when i'm slowing down. when the needle dips down to about 3400, it rattles for a split second then you cant hear it after that