Brakes clack / bang while braking at slow drive

Hello guys, if I drive and brake very slowly with my car (Renault Megane RS), then there is a more or less loud bang every time. You notice this mainly when you are shunting. So far it wasn’t there. In the Renault Forum they think that would be normal – but I don’t want to take any risk when it comes to braking. The bang happens already, if you just tap the brake pedal, so there doesn’t have to be a lot of braking effect. It’s also mainly after load changes. Driving backwards – braking – bang Driving forward – braking – bang Driving forward – braking again – braking – (usually) no bang Driving backwards – braking – banging etc. Here’s a short video with the sound: https://www.youtube.com/watch?v=lMgG9QIPtyk&feature=youtu.be What could that be? Thank you very much.