I've a 08 audi a4 smell of oil inside car but no sign of oil leaking on engine what could it be

 

Might want to check your firewall (between the engine bay and the passenger area) for any missing rubber plugs. There are all kinds of holes in the firewall to route wires, hoses, etc... If a rubber plug is missing then you could get oil smells inside the car. Going to be hard to find as it is pretty tight back there.