Noises from vacuum pump

[GMC-John]

I am getting a constant chirping or squeeking noise from the front of my 1994 6.5. What does the vacuum pump sound like when it goes out? I recently changed the serpentine belt and found that all other rotators were quiet but the vacuum pump made noise when rotating even slowly. The tension pulley was silent and I don't have an idler pulley so I'm guessing I am on the right track. How much fun is it to change this item?

[Robyn]

Hi
The air check valves can make a squeaking noise when the pulley is turned slowly.

Normally though....with the engine running you should not hear much noise....

If you can hear noise from the pump while the engine is running then things are likely ready to be replaced.
Make sure the pump is producing vacuum (A steady 26" of vacuum is normal) if the needle on your vacuum gauge wiggles ...the pump is shot...