Toyota Repair: 2002 Rav4L Whistle from Dash, vacuum line, toyota dealer

Question
My wife drives our 2002 RAV4 2WD Limited with 45K miles.
 
I hear a very intermittent whistle coming from the dashboard.
 
It can happen when starting the car, while driving, but mostly happens when stopped or right after the car is turned off.
It sounds just like a human whistle, one note, varied length, increasing in pitch. As if a gas is venting through a reed from the A/C.
I live on Maui and almost always have the A/C on. I took it to the Toyota Dealer here and they were unable to fix it and never heard it.
 
It's very intermittent and might only happen once a day or less.
 
Although my wife is enjoying the positive attention (the whistling) she's had enough. HELP please. Thanks.

Answer
Steve,

 Could likely be a vacuum line loose or a crack in it under the dash.
Try it with air off and blower switch on separately in different positions. Try it with blower and air off.
Try it with all above and fresh air and air recirculating switch
positions. Try all above with combinations of vent switch in all different positions.(defrost dash, floor, etc.)
One of these combinations will make it go away.
Write them down and check them off because there are a lot
of combinations.


Good luck, let me know.

Tim