Brakes sound loose only when in reverse

Apologies, I posted this before but somehow lost track of that post. This has been bugging me for a while. I've had my prius for a year now and noticed this way back when I first picked up the car from the dealer. But I always assumed that this was normal. Just looking for confirmation that it is (hopefully).

So as the title states, my brakes sound loose when I'm slowly creeping in reverse. Sounds like the brake pads or some lever, but definitely something mechanical moving whenever I press down on the brake pedal. The odd thing is that the sound goes away when I'm in drive, even if I'm creeping at the same slow speed.

Note, I'm not talking about the rattle snake brake accumulator pump, I know what that sounds like.

Anyone notice this or know what I mean? Its hard to describe.

-Dan

 

Sounds the same at any point in the day. I'll try to make a recording of it.