The engine noises I heard from the BMW i8 were ridiculous - not that they were bad but just because it seems so childish. It's like you're a 5-year-old sat on a chair making BROOM! BROOM! noises.
An example is on this YouTube video [0]. First you can hear the electric acceleration, then the driver then slows down and switches on the engine noise. It even simulates the noise of gear changes...