When putting your foot on the accelerator the car does not respond with the same urgency of acceleration. It feels like there is a lag between putting your foot down and the car accelerating, when it does accelerate it feels like a much slower change in speed.
When you accelerate there's a loud hissing sound coming from the engine. The sound is similar to the sound of compressed air from a pump rather than a hissing of fluid dropping on to a boiling surface,
When the engine is running it does sound like it would normally, it can sound like it's struggling to keep running or produce strange noises that sound like it's not running in time with itself.