knocking or vibration

As the title says my Cupra has developed a very wierd knocking noise, its not overly loud but it is rather annoying. It was ok on my way to work Monday morning then on way home it was there. The thing that puzzles me is if you roll down the window it doesnt appear to be heard outisde the car...

Hi, Problem has shown itself this morning on way to work, vibration started about 2mile into journey. While applying power, no knocking, while braking, no knocking, only when cruising and lifting off power. Have problems with steering arms and a warped rear disk, this sounds like it is...