Every PC user will face this problem. We get ‘grinding’ kind of noise from the cabinet. Sometimes this sound would go away after about 2-3 minutes, most of the times it became headace for regular computer usage.
For cooling purposes our computers are equipped with CPU fans, Cabinet side fans, other cooling solutions like fans in SMPS etc. Noise is common occurrence from dust buildup, a bug getting up in any one of the PC fan, a wire getting close to the fan blades, or the fan falling out of the bearing. You must power off your pc in order to inspect the exact reason.
Most of the times fan alignment causes this issue. In this video I explained this issue with clear demonstration.