Clunking/knocking noise when releasing brake pedal???

Hi there,

I’ve got a very annoying but intermittent clunk or noise when releasing the brake pedal or when the car is about to stop. Seems to be associated with the brake pedal but I’m not entirely sure. 

I’ve ruled out the ABS sensor (no light on dash, no fault codes). That leaves no issue with the brakes themselves, either the pedal or somewhere else. Or a suspension issue, perhaps drop links or engine/gearbox mounts (although gearbox mounts are mostly heard when reversing). 
 

Anyone had a similar noise. It’s a taxi and it’s annoying. 😂