Break Sound

at my first 5000 km my yukon started to give an annoying sound comes when applying Breake. several visits to the dealer were conducted at 5000, 7000, 13000, 18000 and now at 28000 km but no good action by them except at 18000 km they do machining to breake discs. the sound was disappeared but at 21000 the sound was graduley appear and the problem comes again with no help from the dealer they were saying you have to do machining again to break discs and replace the break pads at my cost. what do you think guys is this proplem common in your area. for your information i am going rarley off road
 
thanks 
 

typical brake sounds come from vibration of the pad contacting the rotating disc, the use of a anti-vibration to the BACK of the break pad can help as well as ensuring the caliper slides are clean and lightly lubricated. I have also had very good luck with ceramic pads.

Disc brakes usually make a slight noise and can be caused by rust (and moisture), general road debris, or pad dust. Dealer will replace old pads with similar pads in which case the noise is certain to re-occur.
 
Unless you ride your brakes constantly, I am surprised you needed your discs turned at 18k miles. I replaced my pads with Wagner Thermoquiet. They are more expensive but they do work nicely.