2015 fusion hybrid: faint fast beeping sound when climate control is on. with radio off, we can hear this faint beep.

[Charlie01]

With the climate control on, we often hear a faint fast beeping sound. The radio is off. everything is working fine, I turn on the heater, and while sitting in the car in park, we can hear this quick pulsing beep. when we turn off the climate control, it stops. Any Ideas?