Vauxhall Astra rattle problem on start up when hot

Hi there I wonder if you could help me here, I have a mk5 astra hatchback on a 2004 plate with the 1.4 eco Tec engine, when I start the car on a morning it starts up fine but when engine is hot, and I stop the car. Then start car back up engine really rattles badly and oil light stays on, but as soon as I rev the engine this rattle goes immediately and oil light goes straight off, pleas help. John