'03 Camry noise

[NoCal]

I've searched the forum and can't find this specific question or maybe it's just hiding someplace I haven't looked. Either way, here we go:

I have an intermittent noise coming from inside/underneath the dash only when the AC is running. During heat/vent modes, no noise. It sounds like a dove cooing except at the end the sound goes up instead of down...if that makes sense. There's no obvious change in airflow at the vents. I can't catch it doing it to pinpoint where it's coming from but when it happens, I think I can hear a damper or something closing or opening...whichever.

Whatever it is, it's not keeping the AC from working properly right now.

Thanks.