when my car was queeling, it was coming from the bov leaking... check that and vacume lines, i know its got nothing to do with the dump/front but ye, its a skyline, shit happens.
also did u use the gaskets that came with the dump/front/pipe?
i would recommend you go and order factory nissan stuff n put them on... but the thing is, if it was leaking from the gasket i dont think it would squeal