So I there's a noise coming from under the car and I'm sure it's from the transmission. The noise I hear is as If the transmission was loose and moving back in forth . It's a "thump" noise. Hearing the noise literally hurts and I hate it. What can it be?
The hears go in just fine .
And it's a 5speed if it matters

 

More in detail.

Happens only when I let off gas or push clutch in on low rpms.

 

Dual Mass Flywheel.......... 85% sure based on your description

 

Maybe snub mount??

 

This, I already tried the snub mount and is the Dual Mass on mine, I have the V6 so is almost twice as much than the 5 speed 4cyl