Has anyone had a squawking noise from under the hood when pressing the brake pedel?

 

Is this while you are moving or sitting still? How long has it been since the pads were replaced?
Pads usually have a "chirper" built into them so that when you get down to ~5mm, it hits the rotor when the brakes are applied and chirps or squeaks.

 

The internal diaphragm of the brake booster could be failing. Air leakage in the booster can make a noise when you step on the brake.

 

Your profile lists a 2011 RX. Is that still correct? If not, what year, and how many miles?

 

2020 RX-450h with 60K miles