Squeaking Noise at the End of Firm Braking (Especially on Downhill)

I occasionally hear a squeaking noise at the end of firm braking, especially on downhill. The noise is similar to what I hear several seconds after I turn off my Prius. I also feel like there is a slight loss of braking power, when this happens. The brake fluid has never been flushed or bled on my 2010 Prius, and which has 111k+ miles now. Could anyone please tell me what service I should expect to get to resolve this issue? Thank you in advance.