Ok, gonna throw out a few suggestions for obvious things to check on the brakes that someone who knows more will probably be able to tell you are completely unrelated, but what the heck. May as well check 'em while you wait to hear from someone more useful Have you checked: State of wear on the brake pads - are you down to the wear indicators? If so, that could be the source of your nasty noise. Change them asap! State of wear on the brake pads - have they worn evenly? Check all edges of the pad, my Chinese bike had front brake problems stemming from uneven wear. Brake fluid - Is the level in the reservoir high enough? Has it recently dropped dramatically? Can you see any bubbles in it through the sight glass? Cable - Check it's routed properly. Riding at this time of year, and being a Chinese bike, there's a chance that the little metal loop that holds the cable away from the wheel has now rusted through and the cable way have rubbed against the tire and started to wear through. Had that problem on the BMW, which... isn't really surprising, given as it's even less reliable that a Chinese bike. And the disc itself - Does it look at all uneven or warped? Is it showing signs of corrosion? Is there any movement if you try to wiggle it about? We all know that rust is one of the greatest enemies of Chinese bikes, but the big one that people overlook is shoddy assembly and dealer servicing. Most of my problems stemmed from improper assembly so it's worth checking everything is done up properly and fitted straight.