Hello mate, had a few issues when I got my GTi one of which was an intermittent rattle and diesel type clatter at idle, fears were backed up when I got the dreaded low oil pressure warning. Had everything replaced and the car was spot on until I went to pick it up and a very similar rattle came back, after a few days it turned out to be an issue with the variable valve timing. Got the car back and it was running better than it ever had, any flat spots were gone etc. The rattle is now back intermittently when the engine is warm and only at idle or very low engine speeds, a quick blip over 3500rpm seems to stop it (Im guessing something that is getting stuck in the vvt system becomes unstuck) may not be your issue but worth a look. The noise seems to come from the top of the engne, once your on the move it doesnt affect the car at all, but between 3k and 4k there is a noticable flat spot again.