Does a master brake cylinder make a "boiling" sound when failing?

What is your question?

I have noticed that when I am stopped, have the Hybrid in gear and my foot on the brake, that I get what I would describe as a "boiling" sound from the passenger side of the engine compartment...is that where the Master Brake Cylinder is at? Would it make that sound when it is beginning to fail? Or would this be something more related to the Regenerative Breaking system that the Hybrid has?