What is the cause of the rattling noise under the dashboard in my Audi 80?

I have noticed a rattling sound coming from under the dashboard in my Audi 80. It seems to occur more frequently when going over bumps or uneven roads. What could be the cause of this noise?

The most common cause of a rattling noise under the dashboard in an Audi 80 is a loose or worn out air conditioning compressor. This part is located near the dashboard and can be easily accessed for inspection and replacement if necessary.