2005 Renault Megane Weird noise when starting

Engine Mechanical problem
2005 Renault Megane Two Wheel Drive Automatic 28000 miles

Hi guys,

just a quick question. I'm the owner of Renault Megane II Dynamique, 1.6 petrol - Automatic version, year 2005. Everytime I start the engine I can hear rumbling, sounding the same as you start diesel engine. It lasts for few seconds and theneverything is ok. Sometimes I have to press the "start" button twice. The transmition bar is obviously in position "P". Isn't in because of low oil level in a gear box. The thing is, when I park it in a slope surface it doesn't do it.