Air Conditioning problem
2002 Buick Park Avenue 6 cyl Front Wheel Drive Automatic 42,620 miles
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Turning a left hand corner or stopping, we hear a noise that sounds like sand or water shifting. I described this to a parts man who said it sounds like a blocked air conditioner condensate drain. He said it is located on the firewall. If we I turn the automatic air control switch off, the sound disappears.

Do you agree with the blocked drain theory? What do I look for and where for the drain and how do I unblock it?

If not, what do you feel is causing this noise?