Source of engine noise

[ebc]

Greetings,
My 2001 Chevy silverado 1500 had developed a "wheez" that is rpm dependent. I have checked for vacuum leaks with a leak detector but it only works in the ultrasound range. It sounds like it is coming from the alternator or just beneath it. I checked the bearings on the alternator and they felt smooth. (The belt tensioner pulley did need replacement but this did not help the noise). Any ideas? I have not been able to isolate the noise with the stethoscope.
Thanks,
ebc

 

[punisher]

Unplug the connections to the alternator, or pull the "alt" fuse if it has one. Bad diodes can make a whining sound.

 

[ebc]

Quote:

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Unplug the connections to the alternator, or pull the "alt" fuse if it has one. Bad diodes can make a whining sound.

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Will do. The thing still makes good voltage (of course that does not mean it can handle a load).
Thanks,
bc

 

[Tosh]

First rough up the belt with some light sand paper to get rid of any glazing. If there's no change, spray the alternator pulley bearing with WD40 to see if the noise temporarily disappears. (Use a straw in the nozzle so you can pinpoint the spray.) Are you using one of those mechanic's stethoscopes with a tube?

 

[ebc]

Quote:

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First rough up the belt with some light sand paper to get rid of any glazing. If there's no change, spray the alternator pulley bearing with WD40 to see if the noise temporarily disappears. (Use a straw in the nozzle so you can pinpoint the spray.) Are you using one of those mechanic's stethoscopes with a tube?

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Yes. It has a metal rod for a probe. The sound is reminiscent of a car radio (am) when you had unshielded wiring and the generator signal would bleed through.
Thanks,
bc

 

[Tosh]

Isn't there a capacitor to ground that helps to filter this noise? Hopefully it's just that rather than the diodes.

 

[ebc]

Quote:

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Isn't there a capacitor to ground that helps to filter this noise? Hopefully it's just that rather than the diodes.

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The radio does not have to be on. It just has the same sound. It could be the alternator diodes. It started early this spring about the time I replaced the original battery which had cracked and leaked acid.
bc

 

[ebc]

Quote:

---

Quote:

---

Unplug the connections to the alternator, or pull the "alt" fuse if it has one. Bad diodes can make a whining sound.

---

Will do. The thing still makes good voltage (of course that does not mean it can handle a load).
Thanks,
bc

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I unplugged the connector and there was no whine upon starting. Guess its time for a replacement alternator.
Thanks for the tip.
bc

 

[chas3]

use the stethoscope to localize the noise. check the front and the back of the alternator. is the noise louder on either end? also, check the idle and tensioner pulleys again (touch probe to the central bolt). those have pretty small diameters and wear out faster than anything else. dont forget to listen to the power steering pump.