Recently I had a new clutch(Exedy Twin HD) in my Evo VII and noticed it now shudders when downshifting or at launch, but it only occurs sometimes. I'm not sure if it's just me having to use this clutch differently or if something is wrong with it. To stop it shuddering I can either accelerate or push the clutch back in.

What could be the problem?

 

That sounds like a normal twin disc clatter.

 

It's not chatter, it's shuddering the whole car, like a mini earthquake.