Clicking sound in my 2009 VW Jetta

My daughter brought our 2009 VW Jetta Sportwagen home from college this weekend. The engine is making rapid rhythmic clicking sounds (actually not as percussive as a click, but more than a brushing sound) which increase in speed as the accelerator is pressed, whether the car is in neutral, park or drive. The guys at her service station in Bethlehem, PA examined it carefully and drove it around the block, and claim that there’s nothing wrong with the car and that the sounds means nothing. But this seems wrong to me. There’s definitely a noise which is more than just the smooth hum of a VW engine. I opened the hood to look in, but the engine is completely sealed; you can’t see any moving parts except a couple of pulleys and belts. Any thoughts?

You can use a piece of hose as a stethoscope to localize the sound.
Those pretty outer engine covers come off with a couple of tabs or bolts.