Hi all - my Focus does this too. It could be coincidence but whilst on my private property i forgot to put my seatbelt on. When the clunk happened, it set off the red light/beep to say seatbelt not on. Could be coincidence or could be a check to see if seatbelt is on (tho this doesnt explain why it happens on some and not others!). Pete
Its on all focus cars mate, it's the abs brake's checking them selves if you start the car and wait a second then drive off you wont feel the clunk, happens on every focus every time.