Elusive Engine Noise. Crickets?

[cmm47172]

Thanks to anyone who responds to this!
I have a 2008 1500 w/3.7L V6.
I hear a noise that sounds somewhat metallic.
Likely a bearing noise.
The noise also reminds me of the sound of a field full of crickets at night.
I live out in the country.
Sometimes the noise can be heard at idle, sometimes not.
I can always hear it when I get near 2000 RPM.
I removed the serpentine belt and stared the engine.
I brought the engine up to 2000 RMP and could not hear the noise so I figure I'm on to something.
I could not test this way for long as the engine RPM started increasing on it own.
I tapped the gas pedal to get it to idle back down but it kept increasing.
What's up with that?
So fearing I would blow the engine, I shut it down.
However, like I said, the test time was very short and I didn't hear the noise so now I'm assuming it is a bad bearing on either the air conditioner compressor, alternator or maybe the power steering pump or idler pulley.
I replaced the tensioner pulley recently so I know that's not the noise maker.
With the belt off, I could spin all the pulleys and didn't see any play or dragging one would notice with a bad bearing.
With the belt back on the noise is back as before.
I tried listening around the engine with a stethoscope and still can't pin point the noise very frustrating.
The only point I could not get to with the stethoscope is the idler pully.
I was afraid to try to reach that because I didn't want to lose a hand in the fan blades.
That idler pulley could be the culprit. I think I will replace it since it's the least expensive item in the whole deal.
Anyone ever experience this and know how do find the trouble maker beyond what I have done already?
Any idea why the engine would accelerate on it's own with the belt off during test troubleshooting?

 

[chri5k]

Check the torque on all the metal brackets and braces for the accessories on the front of the engine. Loose bolts can allow the bracket or brace to move slightly causing a chirping sound.

 

[cmm47172]

That's good advice! I will check that. Thank you.

 

[cmm47172]

I checked torque and also replaced idler pulley. Still get the noise. Is there a belt I can buy and bypass the ac compressor as a test?

 

[kayjo]

I have had alternators do this. It could just be a bearing. I am not sure what the deal was with the idle. That is worrying, so you lose a belt and your truck runs out of control?

 

[cmm47172]

I would replace the alternator if I knew for a fact that it was the source of noise. Problem is, I can't seem to confirm that. I've listened around the engine with a stethoscope which didn't help. The noise is no louder at the alternator than any of the other components.

 

[Recoil]

Do you have a local AutoZone, O'Reillys, etc.? If so, take the alternator off and bring it in to get tested. They should be able to spin it fast enough to test voltage output. At that time, see if you can hear the noise.

 

[chri5k]

Maybe it really is Crickets. Have you tried an exterminator?