The parking brake is a small drum brake, not connected to the rear hydraulic brakes. Using the brake pedal only acutates the hydraulics, engaging the front and rear calipers if regen can't supply enough stopping power.

My FEH parking brake gets "squeaky" after a while, making a noise anytime I get in or out when the parking brake is set. It sounds like a squeaky suspension, but is really the parking brake. I find it helps to do an occasional low speed stop with the parking brake. By low speed I mean stopping from about 10mph using the parking brake.