I know the PO of my 740i had issues with the UUC brakes he installed. I seem to recall one of them was the pads were moving around a bit and causing a knocking sound. It was solved by changing out to a different pad.
Again - This all pre-dates my taking the car. All I know is that the brakes as they are now are GREAT. NO noise other than my wife squealing if I hit the pedal
real hard...
I have the Akebono (sp?) ceramic ones installed as I remember. That and there was an 'anti rattle' shim/filler involved... I don't have the notes on my car handy now otherwise I'd look it up for you.
Good luck -