constant "eeeeeeeee" noise

[The Wizard of Odd]

Hi I'm new to the forum. I bought an M998 about a month and a half ago from someone else who owned it for a few years and took good care of it. I drive it almost every day and just in the last couple of days it has started making a high pitch "eeeeeeeeeeeee" noise which seems related to engine RPM.
I thought it was belts. But the belts are nearly new and they are tight. Also the sound seems to be worse when the engine is warmed up and it's loudest when at high-ish RPM. Like when driving at 40mph or above. It's just too hard to hear where it's coming from over the roar of the engine. Any ideas?
Now I realize that although my ability to accurately type "eeeeeeee" in a way that describes an unknown engine noise is simply unmatched in clarity, I'm sure it may be confusing to some. But if anyone could take a guess at what a constant noise like that might be and give me some ideas of things to inspect, that would be awesome.

 

[Andyrv6av8r]

Idler pulley bearing?

 

[The Wizard of Odd]

Hmmm.... I like the way you think. I guess I'll take the belts off and see if it turns freely by hand, or if it screams "eeee" at me.

 

[Ajax MD]

Take the doghouse off and open the hood. Have a helper increase the throttle until you can hear the noise.
Walk around the vehicle and attempt to pinpoint the sound.

Idler pulley bearing sounds like as good a candidate as any, or any belt-driven appurtenance such as alternator or p/s pump.

 

[The Wizard of Odd]

that's a good idea. I just need a victim... er I mean "helper". But I think one will be available tomorrow. I doubt it's the power steering pump because the noise doesn't seem to change when I turn the wheel as I would expect it to. But yeah, I'm open to any ideas at this point. The sound is irritating even over the roar of the engine while on the highway while I'm wearing hearing protection. That's not good.

 

[fuzzytoaster]

Does it whine like this? If so you might have ants.

 

[The Wizard of Odd]

Sortof! But that sounds similar to a belt whine. Mine is different, so unlikely to be ants, or a belt. It's more of a constant high pitched "eeeee" sound like this:

 

[Ajax MD]

that's a good idea. I just need a victim... er I mean "helper". But I think one will be available tomorrow. I doubt it's the power steering pump because the noise doesn't seem to change when I turn the wheel as I would expect it to. But yeah, I'm open to any ideas at this point. The sound is irritating even over the roar of the engine while on the highway while I'm wearing hearing protection. That's not good.

I just realized that you could use the throttle lock T-handle under the steering wheel to force the engine to rev up without a Soldier B.

 

[TOBASH]

I see all these movie references, but I would start easy and work your way up... Are you sure its not your wife? (Always wife in my HMMWV. Drowns out the Diesel engine at times).

More Seriously:

Loose belts do this. I had this in my vehicle and actually posted about it. Make sure all belts are tight. Belts can loosen with time.

ALSO, make sure you didn't loose a seal from the water pump or power steering pump. Fluid on a belt will make it slip and scream.

Best,

T

 

[NDT]

Isn’t that the classic Cadillac valve noise?

 

[The Wizard of Odd]

@NDT I don't know if that's it. How would I confirm that? From what I read, that valve makes a "hissing" noise. This is not the sound I'm hearing. More like a constant tone, high pitched squeal that seems worse when the engine is warm and I'm cruising at 40+mph. Also what exactly is the "cadillac valve"? I mean I know where it is, but what does it do? Also, is that a slang term for it? When I search online for that, I can't find replacements. So I'm guessing that it's also called something else?

 

[M35fan]

Welcome to the forum. This is just a stab in the dark, but could it be vacuum related?

 

[TOBASH]

A Cadillac valve is used to control fan on and off. There is a hiss that comes from it. Not loud but also not soft. Wrapping the valve in synthetic rubber sheet helps eliminate the hiss. Much different that a belt whine or a pulley screech.

 

[Milcommoguy]

Alternators can make a whining sound related to RPM. Hows the charging? Shorted / leaky diodes.

Sounds like small siren or low level turbine. Maybe a cat being squeezed, CAM

 

[REF]

Just a guess, but if the power steering fluid gets low, the pump will pull oxegenated oil in and whine at a high pitch. steering still works and sound will vary with engine RPM. Worth checking the level or dropping the belt off the pump to check. I agree the cadillic valve is more of a hiss

 

[BLK HMMWV]

My guess would be power steering pump, but it could be the sound of money flowing out of your wallet

 

[m1010plowboy]

I carry a 4 foot broom stick around to diagnose noise. I thought pop's was crazy sticking the broom handle up to his ear then putting it near the spinning fan blades. A guy must be real careful but if you put a chunk of dowel on an alternator or anything with a spinning bearing....it will tell you things in great detail.

He could listen through a valve cover and tell you which rockers were slapping.

 

[The Wizard of Odd]

UPDATE: I think we figured it out. I had a mechanic friend of mine come over and we went for a ride so he could hear it. Then when we got back he said to spray some WD-40 on the shaft of the alternator. I did this and.... noise gone! We went driving some more at high speed and we noticed that the "eeeeeeee" noise is gone. Of course this means it will return and I'll need a new alternator soon. Although it is charging the batteries, the bearings on the shaft must be almost toast. But while driving we noticed there is actually a 2nd thing producing a high pitched "eeee" noise coming from the drivetrain that wasn't as loud but still noticable. We jacked up the humvee and started turning the wheels by hand and found it. One of the brakes has a little surface rust on the disk and the brake pad just barely rubs it. My mechanics' advice is to just drive it a lot (which I do every day) and the surface rust will wear off eventually with use. So it seems we're getting a handle on the noises.
I tend to get worried about the noises from this thing because I'm not used to driving such a noisy, squeaky, rattly thing. But my mechanic isn't worried about anything he's hearing so it's all good. Now time to invest in a 4 place aviation intercom so I can use my aviation headsets in there and not hear all the squeaks so much.

 

[m1010plowboy]

Operations of old vehicles using 4 senses is almost a requirement. If you don't hear the noise, you'll smell the electrical, see the smoke, feel the heat and won't get to taste the grub at the end of the trip. Good on ya for keeping noises in the PM's.

 

[Milcommoguy]

Rebuild it. Bearings cheap, alternator expensive. CAMO