2000 Passat GLX Knock/Bump

[HiPassater]

Hey,
I have a 2000 Passat GLX and we've had it for about a year now. We're looking to sell it and I believe since we bought the car, it would knock or bump when we come out of a stop. This only happens if I apply the accelerator firmly. If I come out slowly from a stop it does not occur. I heard something about it being an "engine bump" and is somewhat a normal thing. Can someone please help and let me know if this is true or if there's anything else I should be wary of? It doesn't occur at any other time outside of from stop. thanks for any help.