What could cause a high-pitched whine behind the dash in my Ford Focus?

[Noah41]

My 2017 Focus has started making a faint but constant high-pitched whine that seems to come from behind the dashboard. It’s there with the key on, engine running or not, and it doesn’t change with the fan speed. I’m worried it might be a sign of a failing blower motor resistor, but I’ve never heard one make this kind of noise before.

[BrianG]

I had a similar thing in a Focus once. a faint high pitch behind the dash that wouldn’t care about fan speed. turned out to be the blend door actuator acting up. it would start when the climate control woke up and would squeal a bit as it moved.

[Andrew10]

I’m leaning away from the resistor idea here. the blower resistor usually shows up as a change with fan speed, not a constant tone. a failing actuator or a loose connector inside the HVAC box can make a constant high pitch behind the dash.

[Jonathan7]

I did a few quick tests by flipping AC on and off and toggling vent settings. the noise stayed the same, which pushed me toward an actuator issue rather than the blower itself. still not sure, but it helped me stop assuming it was the resistor.

[MadisonAA]

Does the noise change when you switch between dash vents and floor or defog modes?