Have 1998 gs3 168k and sometimes there is buzzing sound on the driver side only hear it when i slowing going to a complete stop and left turns...please help

 

brake master cylinder?

 

Beez. Youve got beezzzzz But seriously its your brake booster or something that has to do with your power brakes. If you pump the brake pedal repeatedly while the car is running in park you should be able to recreate this sound. Totally normal.