My car has a weird rattling and im starting to think its the clutch. While im driving it will rattle pretty loud from what sounds like directly underneath the shifter. You cant hear it from inside but if u have the window down it is very noticable. I just laid down underneath the car to listen to it while it was running and sounded like it was coming from underneath the shifter. While driving it rattles and sometimes while idling it is really loud but as soon as i put the clutch in to shift gears it goes away.

 

What you are describing as a rattle, I call a knock.

If it goes away when you push the clutch in, it's your throw out bearing. The noise you are hearing is the slop in it which is generally louder at idle.

So yes, more than likely you need a clutch too.