Since regen braking takes care of 90% of the braking in the Model 3, the brake pads don't see much wear at all. Due to this, the pads develop surface rust, especially if you experience a lot of rain and/or humidity in your region. The brake rotors are also rotating slightly when you turn the wheel, so if the slightly rusty brakes are applied at that time (either with brake hold or with your foot on the pedal), they will make noise as the rotor rotates across the uneven pad surface.
To alleviate this, switch Regenerative Braking to Low in your settings, bring the car up to >30 mph or so, and (safely) hard stop a few times. The results are immediate and apparent, so if this isn't working for you it may be something else.
It's worked for me the last ~4 months, of which April is breaking all-time records for rain in Seattle. Overall though, it is within normal spec according to the SC.
