Glass bottles clinking together???

[Duane, Andrew]

My 2000 A6Q has suddenly developed a very strange noise. When I close
one of the front doors, there is a sound that is *EXACTLY* like a couple
of glass bottles clinking together. The sound is coming from the front
of the engine compartment, maybe down near the A/C compressor. It's 100%
reproducible, even by pounding on the front of the car a little.

What in the world would be down there that sounds like glass?