Hi all,
I have a 2005 Explorer. If your car has dual climate control and is making an intermittent "whooping" or "siren" sound in the back, you need to replace your HVAC Heater Assembly module. You can log on to Official Ford Parts Site | Buy Motorcraft & OEM Ford Parts Online | FordParts.com. Input your make, model and then HVAC, Valves....and you will see the drawing. The part is $250. Your Ford Dealership will charge $800 to replace it. If you are a mechanic or mechanically inclined, you can replace the part yourself. It's funny how the dealerships can not seem to figure out the problem. It's also interesting to note when I ordered the part, somebody else tried to buy it from the Ford dealership. It sounds like a lot of folks are having this problem. However, Ford doesn't want to admit that they have a faulty HVAC system. In any case, I've posted a video if you want to see the part and try doing this yourself.