2013 v.w. jetta noise when accelerating (Please read description

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Whenever I accelerate (like from a stop sign), the engine makes a very loud noise that sounds like roaring and goes in and out for a few seconds before stopping completely. The noise is very loud, almost like a motorcycle, and can be heard from nearly a block away. I only hear the noise when accelerating and not when starting the car. The noise lasts for about 5 seconds after pushing the pedal, sometimes longer. My car is nearing 100,000 miles.