Compressor for air conditioner noise

Why does my compressor make a noise like dadadadadadadad…it works fine but makes the noise

94 gmc 2500

There are several sources that could make that noise.

  1. Bearings on idler pulley are failing
  2. Compressor bearings failing
  3. A/C clutch bearings failing. You could give it a short squirt of WD-40 around the clutch bearings and see if the noise changes. If yes, that could be the source of the noise. Don’t get it on the belt.

Thank you Sir