Air Conditioning problem
2004 Chevy Epica 4 cyl Two Wheel Drive Automatic 53000 miles

Hi
in the first 15 min after starting my car, if i press on the accelerator i am getting strange sound from my dashboard. the sound is like water half filled in a bottle and shaken vigorously. the sound stops after about 15 to 20 minutes..

My repair centre says they need to open the dash board and they it costs 400 USD.

is it true and what is happening...

appreciate ur help..