it could be the belt tensioner as i have just had mine replaced and the rattling noise stopped. it just rattled on n off while idling. if its coming from the left hand side of the engine wen standing at the front then it could be tht. just sharing my thot on wat it could be if it helps
The auxilliary belt tensioner is the usual cause of rattles at tickover but it's a bit odd that dipping the clutch stops it. It could be that dipping the clutch raises the tickover slightly as the tensioner rattle only happens at a very low tickover at first. If the rattle is from the drivers side when you look under the bonnet it's most likely the tensioner as it's at this end, the clutch is at the other side.