High Pitched Hum (squeal)

Hutch · January 9, 2003

I have developed some sort of high-pitch hum on my '02 2500HD 8.1/Allison Crewcab shortbed with 10k miles. This sounds like the noise you get when you run a wet finger around the top of a crystal glass. It only happens between 35 & 45 MPH or so and only when I barely have my foot on the accelerator, just enough to maintain speed on a flat road. If I let off the gas, it slowly goes away (as the speed drops by about 5 MPH). It also goes away if I accelerate or apply the brakes. I cannot pinpoint the noise as it is one of those "droning" sounds that just grabs your ears and ties 'em in a knot.

Any ideas what this could be?

Thanks,

Hutch ???

January 10, 2003

Tire Whine?

Gunruner · January 10, 2003

Did it just start one day? If so, I'd look at the intake hoses and clamps and see if someting is loose and is causing the sound. I had a sound like that when running an air cleaner box without the element(don't ask). Made the noise at light throttle and low rpm. Just a thought, good luck.

SWLA · January 10, 2003

Hutch,

I had a similar noise a few weeks ago. Very high pitched, almost like a tuning fork. I only noticed mine a low speeds. Took the dealer 2 days to find it. Service advisor said they were able to reproduce it, but no one in the shop could figure it out. Had to call a someone up the chain. Eventually got it fixed. Here is what the repair order said:

Transmission output shaft seal dust boot rubbinng driveshaft causing noise. R&R driveshaft to confirm noise. Reinstall driveshaft and reposition F1280.

No noise since. This was at about 19,000 miles.

Hutch · January 10, 2003

Yes, this just started one day but it seems to be worse sometimes. I'll check the intake hoses and airbox.

I don't think it's tire whine.

It does sound like a tuning fork!

Hmmmm, driveshaft.......ya know, now that you mention it, it does sound about the same pitch as the driveshaft would make if you thump it with a wrench. I'll see if I can see anything down there, otherwise I'll have the dealer check the dust boot. Thanks, SWLA, for sharing that info! :thumb:

Hutch

ehart · January 16, 2003

Greetings,

I have just completed ripping out all my stock speakers as well as the in-dash 6-disk CD player from my truck that has about 3500 miles.

Shortly after the install, I noticed a high pitch sound that I thought was coming from my speakers. The type of high pitched sound that changes with the RPM of the engine, which is usually caused by bad ground wire. After some de-bugging, I turned off the stereo and the sound was still there, so I assumed it was the turbo or another normal engine noise.

Now after reading this post, I am beginning to wonder….

Now that I am aware of the high pitch sound, it seems much louder

sutak · January 21, 2003

I have developed some sort of high-pitch hum on my '02 2500HD 8.1/Allison Crewcab shortbed with 10k miles. This sounds like the noise you get when you run a wet finger around the top of a crystal glass. It only happens between 35 & 45 MPH or so and only when I barely have my foot on the accelerator, just enough to maintain speed on a flat road. If I let off the gas, it slowly goes away (as the speed drops by about 5 MPH). It also goes away if I accelerate or apply the brakes. I cannot pinpoint the noise as it is one of those "droning" sounds that just grabs your ears and ties 'em in a knot.

Any ideas what this could be?

Thanks,

Hutch ???

Hutch,

I have a 2001 K3500 CC dually with the 8.1L/Ally combo. I experienced a droning sound as well. Eventually I could relate it to the engine rpm. At around 2100 rpm this noise was the most noticeable at any gear.

I took it to the dealer and they installed counterweights on the exhaust. The first time it didn't work. After that they got another set of counter weights and placed them somewhere else on the exhaust. Finally they resolved the problem.

good luck,

Larry.

jr.parrish · January 21, 2003

I have the exact same problem on my 99 1500 w/5.3. It really hums load at 41MPH and it only started about a month ago (48K miles). Its driving me nuts.

Hutch · January 23, 2003

EHART,

My pitch does not change at all, not with speed, diff gear or anything. But it only "comes alive" between 35 & 45 MPH and only when I'm just barely touching the accelerator to maintain speed. It's definitely a harmonic of some type, I just can't figure out from what.

SUTAK,

What are "counter-weights" that they put on the exhaust? I was crawling around under the truck tapping on different things and the exhaust certainly has a similar tone to the harmonic I'm getting.

Hutch

odoh · January 25, 2003

There are varied responses submitted for your consideration. So, I won't add another ~ but noticed you have an 8.1L engine. What is oil consumption like?

~ odoh

04Chevy2500HD · January 28, 2003

Mine makes a high pitch squel since the day I purchased it. It only makes it for about the first 15 min of engine warm up. Mine sounds like a exhaust noise or something like that. When I get some time I will take it to the dealer. Maybe sometime next week.

David