NOOB: Strange "Whistling" Noise?

[FlameRed]

Once again the NOOB must come to the collective to get advise.

Recently, I began hearing a whistling noise that I have been unable to track down. At first I thought it was bad belt(s) or a bearing going out, but now I think it is something else.

It sounds like a whistle to me. Maybe a vacuum leak?

The weird part, is that it seems loudest in the driver's seat. Don't hear it much in the engine compartment.

My two most recent projects were:

• Upgrading from a TH400 to a 4L80
• Replacing the aftermarket evaporator for the AC

But to be honest, this is a new noise, that started in the last few weeks, well after both these projects were finished and the noise was not present after either project completed.

Here is the weird part - to hear the noise, the following conditions must be met. The noise is not always present!

• The engine MUST be up to operating temp. Cool engine, no noise.
• Can be hear while driving or sitting in the driveway with the engine hot.
• The AC must be on.
• Throttle must be at idle or decelerating - very low throttle, or no throttle. Noise not present at power making position somehow?

I thought it might be the fan on the evap that I replaced, but if I let the fan on, with the engine off, no whistling. Also, the pitch of the whistling does not seem to change if I change the evap fan speed. And why would the sound go away at mid or full throttle?

Is this sound something familiar that a NOOB would not know?

 

[mgFray]

See your left side of the dash, there is a meter that detects how dirty the air filter is. If you broke the hose it could whistle, as it'll let air in through the hose.

 

[NDT]

Maybe the Cadillac valve.

 

[Mogman]

Maybe the Cadillac valve.

If it is one would think it would change whilst turning the steering wheel back and forth, something to try, although the AC having to be on seems to rule out everything but an AC issue, but.....

 

[Gcelevator]

Sounds exactly the same as my RedDot AC evaporator fans.

 

[Mogman]

Sounds exactly the same as my RedDot AC evaporator fans.

OK, seeing as you have a 60A alternator it just might be the voltage is sagging at idle and causing the evap motor to get to a speed that causes it to make that noise, that would explain why it only happens at or near idle, maybe time for an alternator upgrade!

 

[Gcelevator]

OK, seeing as you have a 60A alternator it just might be the voltage is sagging at idle and causing the evap motor to get to a speed that causes it to make that noise, that would explain why it only happens at or near idle, maybe time for an alternator upgrade!

No mog, i do have the 200 Amps. The OP might have the 60 Amps. Yes, my fans make a high pitch noise; like a combination of high speed and high pitch air through the thin blades. Hard to describe but similar to OP's, probably louder.

 

[FlameRed]

No mog, i do have the 200 Amps. The OP might have the 60 Amps. Yes, my fans make a high pitch noise; like a combination of high speed and high pitch air through the thin blades. Hard to describe but similar to OP's, probably louder.

Yes, I do have the original 60 Amp generator. Sounds logical that it would be the evap fans since the sound seems to go away with the AC off.

I am just wondering why the sound is present with the engine running, but if I shutdown the engine and I have the evap fans running (any speed), the sound is not present. Maybe it needs the compressor running, engine to run, also for the fans to make that sound?

I got to admit that it sure sounds like the sound is comimg from the inside of the cabin, not the engine compartment.

 

[Mogman]

No mog, i do have the 200 Amps. The OP might have the 60 Amps. Yes, my fans make a high pitch noise; like a combination of high speed and high pitch air through the thin blades. Hard to describe but similar to OP's, probably louder.

SORRY!! I was referring to the OP, he was the one that said it only happened with the AC on and at idle, I will be willing to bet if he puts a voltmeter on the truck and watches the sound (caused by the harmonics of the fan blades turning at a particular speed) it is directly affected by the voltage, I flubbed up when responding to your post.

 

[FlameRed]

What is the recommended 60 amp generator upgrade but be able to keep the twin V-belt setup? Or is there a kit for a serpentine belt system?

I found a couple of You Tubes of folks that went to a 60 amp alternator but that won't increase the amps. And I see kits for a 160 amp alternator but that is for a serpatine belt system.

 

[Gcelevator]

SORRY!! I was referring to the OP, he was the one that said it only happened with the AC on and at idle, I will be willing to bet if he puts a voltmeter on the truck and watches the sound (caused by the harmonics of the fan blades turning at a particular speed) it is directly affected by the voltage, I flubbed up when responding to your post.

No need to apologize.

 

[Gcelevator]

Yes, I do have the original 60 Amp generator. Sounds logical that it would be the evap fans since the sound seems to go away with the AC off.

I am just wondering why the sound is present with the engine running, but if I shutdown the engine and I have the evap fans running (any speed), the sound is not present. Maybe it needs the compressor running, engine to run, also for the fans to make that sound?

I got to admit that it sure sounds like the sound is comimg from the inside of the cabin, not the engine compartment.

In my case for the 1st couple of minutes, the fan does not make that noise. As soon as my generator gauge hits the green line the RPM on the fan increases and makes the noise.

 

[Mogman]

Normally the 200A uses three belts, I have a modified 200A (conversion) mount,, IIRC the mount moves the alt back just enough to use three belts on the alt and only one on the PS pump (the three alt belts also go around the PS pump) that leaves the fifth groove open on the crank pulley for the AC comp.
I also have a 100A alt that will bolt up to your 60A mount, not sure yet if I want to get rid of it, dang things cost about as much as a 200A.
I would be interested in your feedback after putting a volt meter on your truck and seeing if that sound corresponds to changes in voltage.

 

[Mogman]

In my case for the 1st couple of minutes, the fan does not make that noise. As soon as my generator gauge hits the green line the RPM on the fan increases and makes the noise.

You are lucky enough to hit that "sweet spot" under normal voltage conditions, you could try a resistor to slow the fan down just a little bit.

 

[FlameRed]

No mog, i do have the 200 Amps. The OP might have the 60 Amps. Yes, my fans make a high pitch noise; like a combination of high speed and high pitch air through the thin blades. Hard to describe but similar to OP's, probably louder.

In my case for the 1st couple of minutes, the fan does not make that noise. As soon as my generator gauge hits the green line the RPM on the fan increases and makes the noise.

Thanks - so I think you are saying that even if I upgrade from my 60 Amp generator to a 200 amp, the sound will still be present.

I put a voltmeter on it and report back as soon as I can...

 

[Mogman]

Yes, I do have the original 60 Amp generator. Sounds logical that it would be the evap fans since the sound seems to go away with the AC off.

I am just wondering why the sound is present with the engine running, but if I shutdown the engine and I have the evap fans running (any speed), the sound is not present. Maybe it needs the compressor running, engine to run, also for the fans to make that sound?

I got to admit that it sure sounds like the sound is comimg from the inside of the cabin, not the engine compartment.

With the engine not running the voltage would be even lower than at idle, moving the evap RPM lower than the "sweet spot" that causes the harmonics, when you rev the engine up it moves the evap RPM above the "sweet spot" Does the evap have more than one speed???

 

[FlameRed]

I finally got around to hooking up a digital VOM at the batteries and drive it around. The voltage with the engine running, any speed, any load, was pretty consistent at 27.3 to 27.4 volts. Extremely stable - pretty much the same within 0.1 volts between idle or 2000 RPMs, or stopped at a light or cruising along. With the engine off but in run position, it was slightly over 24 volts. So I do not think it is generator related, like a drop in voltage at low RPMs or idle.

I confirmed that the noise was present no matter what the AC fan speed was. Changing the position of the AC fan speed did not impact the sound, or make it go away or start.

Also, turning off the engine fan clutch using that manual switch @Mogman suggested did not change the sound or make it go away or start up.

It really, really sounds to me like a belt squeal, but I am not sure why the AC belt squeal would be louder in the cabin than listening to when the hood is open!

So I plan on changing all the belts as soon as the Florida inferno goes away and I will see if that cures it. Had that planned anyway. If that does not cure it, I will take apart the AC evap and see if there is something interfering with the motor.

Of course since the aftermarket evap is a Chinese product, it could be just a POS!

 

[Mainsail]

I wish someone had a video of the company staff meeting at AMG when it was announced they wanted to make the HMMWV a civilian vehicle... Probably never see a herd of engineers who suddenly had to leave for an important phone call move so fast.

 

[FlameRed]

Of course since the aftermarket evap is a Chinese product, it could be just a POS!

Bingo! Found the cause of the sound. The plastic evaporator fans gernaded and shreaded themselves into mess of shrapnel

I found possible replacement fans but it might be easier just to rip out the whole Chinesiumcrapulum and replace the unit.

At least the Florida Inferno is outta here!