Over the last couple of weeks, I have noticed a screeching noise every time I engage the exhaust brake function. This truck has a variable-geometry turbo that closes down the VG mechanism after a couple of seconds' trailing throttle. This assists decel of the truck when towing or heavily loaded. The problem started only occasionally during exhaust braking mode, but now the screech occurs every time, and is now even beginning to occur under hard acceleration when the turbo is putting out high boost. Has anybody else out there had this problem on the 6.7L Cummins? I am theorizing that the thrust bearing in the turbo may be going out, and would require an expensive repair. Are there other possible causes for the screeching noise?