Rust mainly as already stated, burning oil , rub the oil see if theres any flakes in it if so its bad, rattles / bangs . heres a link to a more in depth guide, its literly stickyed at the top of the thread haha use the search bar !
Also check for accident damage as a lot where imported like this then fixed water lying in the boot is a common problem but easy fixed also just check the engine code and make shure it is a b16b in it ..