2003 1.8T clicking when coasting

I just bought a real creampuff 2003 1.8T 5spd with an unknown problem which causes audible clicking when the car is moving, but not under acceleration. When I accelerate, everything is running seemingly perfectly... quiet, powerful, smooth. But... as soon as I let my foot off the gas there's an audible clicking continuously from somewhere under the hood. The sound gets softer as you apply engine power, and again, quiet when accelerating. I'm hoping to hear it's something as simple as u-joint, or boot, etc... But I have sneaking suspicion it lies somewhere deeper...

Any ideas?

Thanks!
JT