I wonder if it refers to uneven wear on the same caliper, uneven wear between sides you would probably feel pulling to one side.

Possible sticking caliper piston or caliper slider if a sliding caliper design, worth getting a proper mechanic to service the brakes correctly, which almost no-one does now...strip inspect cleanup and the most important part, lube up with the correct brake grease.

If a slider is sticking it means one pad only gets pressed hard against the disc instead of a free moving caliper equalizing pressure between both pads, a piston sticking on a twin piston non sliding caliper will produce the same result.

Might be that poor quality pads were fitted at some point which won't perform well, never the most economical choice in the long run, and a remote possibility that some cheap skate replaced one side only.

Edited by gordonbennet on 28/09/2016 at 12:51

You don’t say front or rear (nor if it’s side to side or one side). If front, then GB covered it. If rear it could be hand brake not fully releasing.

Worn pads.

Worn disks - scored

Rusty disks

Worn slide, rusty slides

Sticking calipers.

Dirt between pad and caliper

Strip down and examine jobbie. If anything like my son's 318i, £££s..