I have had a problem with my brakes squeaking on my 400h. The rather loud squeak/squeal occured mostly when I was backing up and was loud enough to attract attention from passers-by.
The car has less than 4,000 miles on it.
I brought it into the dealer earlier in the week and was told they could find nothing wrong so I asked to speak with the service manager and expressed my dissatisfaction with this.
The service manager had me drive back and forth demonstrating the squeak and agreed that the noise was unacceptable.
Today i brought the car back to the dealer so that they could investigate the brakes and they discovered the front rotors had cracked. These were replaced.
Just FYI, when I asked the service guy why this would happen in a car with so little mileage he told me they had seen a few cases of cracked rotors in the 400h.