I have a 2008 WRX - fully stock. A few months ago, out of nowhere, the heater started to make a constant high-pitch whistling/horn type of sound. It seems to only happen when the climate control level is at or near full-blast, is on floor and vent, and it seems to be the loudest at speeds over 40 mph. Sometimes it will stop when the car is at idle and start back up as soon as the car takes off. I took it to the dealership and they replaced the blower motor.... but it's still doing it. After a little more investigation, I'm pretty sure that the noise is coming from the dash closer to the driver side. It's such an irritating noise! Please help!