Thanks for the update, given they are 30k plus you have done well if the pads disc's still have lots of material left. The lip test is a quick and dirty measure by the way, they should be measured with a micrometer with the wheel off as this will tell you exactly how much life is still in them.
Subject to breaking and driving profile it is normally two sets of pads to one disc and including the rears as they can wear just as fast as the front, but many do not follow this on modern cars with electronic stability control etc.
Going back to the issue, it may well be that they are now due a new set of pads, that the guide pins are now very dirty, which affects how the caliper floats, it could be dirt etc built onto the frame of the caliper, sometimes the anti squeal springs lose some tension, it amazes me that people seldom change then with the pads, they are cheap item. The answer in part is to leave it until the pads eventually go via the CBS on the Idrive, it will tell you how much life they have in them. Stripping down now will help to find the issue, but personally I would leave it till the pad change.
Always said I would go back to a 6 series