I have a t5. when I and bogged down a lot or even a little. like when i'm in 4th gear and it wouldnt hurt to shift to 3rd. or when going up a steep hill in a high gear when I give it gas there is an awful grinding sound coming from under the car and the car will shake. If kinda sounds like the clutch is slipping but I dont(or haven't noticed) and loss in power. And when I take off from a dead stop the car will shake as i'm letting out the clutch. anyone have an idea of what this could be? Also when I'm winding out the rpms or just cruzing in the right gear for the speed the noise is not present and the car drives fine.

 

The best way I know to describe this is, it sounds like your brake pads have no pad left and you hit the brakes. the metal to metal sound.
also a guy at work (i work in a shop) said maybe I should run higher octane gas. it could be valve chatter runing through the drive train. Could it be something like that?