Engine started making a noise, initially it sounded sort of flutter like, (can't think of a better description), so thought it was something flapping about or something underneath. It eventually became more apparent as a tappet like noise. I checked the oil, and it was very low, below the minimum - took 1.5 litres to get it up to max. Seems that at some point, it stopped displaying the dashboard indicator when the engine starts without me realising. It's still making a slight noise although nowhere near as loud. What sort of damage could I have caused? It's due for a service anyway, so the oil is due to be renewed, will that help?