What thah! Is it the transmission or is it the engine?
If the car is on drive or overdrive and i suddenly step on the gas the car will make this loud single knock noise and it feels like something right underneed the ash tray and the console area jumps up and hits it and then it keeps going, This is only when i'm not moving and then step on it. If i'm moving already, it wont make that noise and it wont jump.

Is this serious? Whats wrong?

 

Sounds like a bad tranny mount. This topic has been covered many times on the boards. Do a search and you'll find plenty of info. on this.