Loud squeak/squeal noise when lifting off the brake pedal

I recently purchased a new (to me) 2010 prius and I've been noticing that sometimes, but not always, I hear a fairly loud noise when lifting my foot off the brake pedal. It sounds like a squeak or squeal, and I want to say I can almost feel a tiny bit of resistance in the pedal when it happens though that could be in my head. The noise does NOT occur when pushing down on the pedal (only when lifting), and it seems to only occur when the car is stopped.

I also hear what sounds like an electrical pump sound after several pumps of the brake, but I'm not too concerned about that one as that seems like normal pump noise. The squeal definitely seems off to me, however.

My car is not applicable for the brake accumulator recall (I checked, build date of 5/10).

Is this noise abnormal? Is it worth taking it in to the dealer?

 

Ok...?

 

Thought I'd update in case this helps anybody down the road.

Toyota ended up replacing the brake actuator assembly, which was a $3K job including parts and labor (ouch)! Thankfully, my car is still under warranty so it was covered. I'd be pretty livid if I had to pay that much to fix the brake system.

Anyways, the groan noise is gone after the replacement.

 

That was a recall for the brake accumulator, not the brake actuator. Also my car was not in the affected VIN range (my build date was late 2010).