My car makes a LOUD noise when i accelerate, whats wrong with it?

I have a 2002 dodge neon, and when ever I accelerate over 1.5 rpm it makes a Muffler noise and it vibrates the interior of the car, like my phone is on vibrate,,, but its not the muffler or the exhaust system because i got it checked and i installed a new catalytic converter. The noise is mostly heard inside of the car and it vibrates really hard,,it doest vibrate like if my alignment is messed up, because my alignment is fine... PLEASE HELP.Thank you