Knocking sound

Hey,

Just had my clutch and flywheel changed. Before the change there was a knocking sound coming from the engine bay when the clutch was released and it disappeared when the clutch was depressed.

Now I have a knocking sound while pressing the clutch and while it is depressed, I even feel something vibrating on the clutch pedal while doing this. The sound is fairly loud when the engine is completely cold and it is almost unnoticeable when it's working on running temperature.

Any ideas on what it could be? 

It's the 2007 1.9 TDI 77kw version.