2005 Sub - High frequency sound at idle.

Machine · June 17, 2005

The vehicle: 2005 Suburban Z71

The setup: Sitting at a red light idling and/or accelerating from a stop.

The noise: Sounds like medium to high pitched feedback produced by an amp. The sound lasts anywhere from a fraction of a second to a few seconds.

Location of sound: Your guess is as good as mine

Things that I’ve ruled out: The feedback is never too loud and has no correlation to the stock stereo. In other words, the noise will sound with the radio on or off, and it remains at a constant volume no matter what the volume is on the radio. The sound does not appear to be produced by a belt, or brakes, or the air conditioning. It happens about once a day and has never been heard while actually cruising – only while at a stop, or under acceleration. It’s not a noise that hurts your ears, but rather a medium high pitch that just sounds really odd.

Ok, that’s the best way to describe this noise. If you know what it is, please let me know. Thanks.

GM Dude · June 24, 2005

The vehicle: 2005 Suburban Z71

The setup: Sitting at a red light idling and/or accelerating from a stop.

The noise: Sounds like medium to high pitched feedback produced by an amp. The sound lasts anywhere from a fraction of a second to a few seconds.

Location of sound: Your guess is as good as mine

Things that I’ve ruled out: The feedback is never too loud and has no correlation to the stock stereo. In other words, the noise will sound with the radio on or off, and it remains at a constant volume no matter what the volume is on the radio. The sound does not appear to be produced by a belt, or brakes, or the air conditioning. It happens about once a day and has never been heard while actually cruising – only while at a stop, or under acceleration. It’s not a noise that hurts your ears, but rather a medium high pitch that just sounds really odd.

Ok, that’s the best way to describe this noise. If you know what it is, please let me know. Thanks.

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I have the same noise in my 2005 GMC Sierra Crew and can not figure it out. Wish someone knew of a service bulletin on this. If I here anything, I'll let ya know.

Machine · July 26, 2005

FYI for anyone who happens to have the same issue:

The noise was caused by the thermal expansion valve on the rear air conditioning system. A bulletin was issued to GM on June 28th stating the problem and fix for the issue described above.

Thanks.

GM Dude · August 2, 2005

Took my 2005 GMC Crew to the dealer for a high pitched noise recently. First they tell me it could not be duplicated so I pushed it a little and they test drove the truck with me and then they heard it. They kept the truck for 2 days and called me and told me it was the thermal expansion valve and the engineering team was working on a fix. I explained that it made the noise even without the air on and they told me it would make the noise even with the air off. Wait, the bulletin that he gave me says when the "A/C compressor is engaged".

Well, I decided that I would do my own investigating into this matter. First, the noise happened at about 1000 to 1500 RPM with the transmission in gear. So I had the wife in the truck, in gear, A/C off, parking brake on and raising the RPM up to between 1000 and 1500. I heard the noise and it appeared to be coming from the driver side area. Then I narrowed it down to the brake booster so I put my hand on the check valve and it was vibrating and making the high pitched tone. Lowered the RPM and the noise disappeared as well as the vibrating of the valve. I just so happened to have a check valve from a '92 model Chevrolet so I installed it. Lo and behold, NO more annoying high pitched noise.

I have been putting up with this noise for about a 2 months, took it to the dealer for 2 days and it took me 5 minutes to find and correct the problem.

For some reason this particular check valve at 1000 to 1500 RPM resonated just right to make that high pitched noise that was so aggravating.

Calgary GMC · August 3, 2005

I've got the same problem with mine. Does anyone know if the loud A/C Clutch engagement is also part of the repair? I find when my A/C engages, the clutch makes quite the loud 'Thud'. Even at highway speeds, you can certainly tell when the A/C is engaged! I've never had a vehicle that makes such a racket when you've got the A/C on.

Thanks