Anyone know what this noise is?

Once you participate 5 time on Prius chat you can post links... Your croaking problem is probably not too big of a deal, but need more info. Any warning light. How many miles on that car?

 

There is a Prius brake noise sometimes referred to as the quack, bark, or honk. There are small valves in the brake actuator, and in some circumstances brake fluid can squirt through a part-open valve and honk it like a saxophone reed.

If you have a 2010, there was an update to the brake ECU firmware to make it honk less, as described in T-SB-0363-10. It gives the firmware version to update to, separately for 15-inch and 17-inch wheel cars. If your 2010 is a V, then you probably want the 17-inch version, F152647128.

If that is not the version currently reported by your brake ECU, the dealership can reflash it, probably charging for about an hour of shop time. If you have a bunch of stuff in the hatch area, you can save them time by having that cleared out first, because their procedures require them to support your battery with a power supply to avoid any risk of power loss during the reflash.

It is possible for a car with the updated firmware to still honk some (or for a car later than 2011 to still honk some). If that happens, the next thing I would try would be the "long form" brake bleed procedure, the one meant for getting any bubbles out of the underhood hardware and not just the lines to the wheels.