23 Sierra 2500HD 6.6 Gas/6L90 drivetrain whine

15DenaliSummit · December 6, 2024

So I’ve had my 23 HD for a year and a half now, and at 10k miles a whine started at 80 mph when under load and would stop when I let off the throttle. Had a local dealer look at it and they claimed it was my toolbox…. It started getting worse and I brought it back to the dealer I bought it from, obviously without my toolbox or tonneau cover. Now it comes on at 75mph and is louder, the lead tech took a ride with me and thankfully heard the noise. But the dealer is now claiming it’s normal operation because they don’t know where the noise is coming from. Has anyone else had this noise yet and any solution to it?

Another JR · December 7, 2024

A mechanical whine (as opposed to an air whistling sound) that is there when applying torque and goes away when coasting sure sounds like drivetrain gear noise to me. I would suspect the rear axle ring and pinion set or bearings rather than the transmission, especially if the tone varies with speed and not with gear changes. Have you looked at the rear axle oil level and cleanliness?

15DenaliSummit · December 8, 2024

Another JR, so when it first started the noise I checked the rear axle oil level, and had to add 1.5 quarts which wasn’t too lovely to find out at 10k miles. But both dealers have said that the noise is not coming from the rear axle. Where the truck is now they are saying it’s from the transmission area but can’t find where the noise is coming from/they don’t want to tear into it without GMs approval. They’re saying to take it back and bring it back when it gets worse, it’s not really installing the most confidence in them. We’re going to talk more on Monday because I’m politely but firmly refusing that “repair” and may have to start making a fuss with GM about it. A coworker mentioned he read on a facebook thread that the newer 6L90s have been having a highway speed whine very similar to mine and a transmission builder that tore into one couldnt find out why it was making the noise. So we shall see what the dealer has to say on the next steps tomorrow.

Another JR · December 8, 2024

Keep us posted, and good luck. So far my 2021 with 12k miles is still quiet. I don’t tow heavy, though.

UWSkier · July 21, 2025

I know this is an old thread, but I'm at 21k miles on mine and I have a noticeable differential whine when on the power. I may also have a driveline vibration at 75MPH but I think that's a harmonic thing with the tires as it doesn't seem high enough in frequency to be rotating with the driveshaft. I have about another 500 miles to go in this cross country camper tow I'm doing, then it's back to the dealer... again...

I bought this truck to tow hard and heavy, and it does, but for it to have so many driveline issues in under 25k miles is awful.

15DenaliSummit · July 21, 2025

UWSkier

I forgot about this post so I’ll give you an update.
they did nothing for me but opened up a case with GM, I guess a GM engineer decided it was a normal noise so that’s all they could do for me. I’m just shy of 31k miles now and the noise is getting slowly louder, accompanied by harsh shifting in all gears now so I’m going to call the dealer tomorrow and get on their case again. This will be the third time going in for this issue and thankfully with CTs pretty stout lemon laws I can still go for it after 2 years/24k miles if the problem originally started within that period. Going to keep updating as I’m going through this round of nonsense.

The Hoss · October 13, 2025

I've had my 24 6.6 gasser for almost 2.5 years. I had the same whine at 130km/h (80mph) since new. My buddy is a Chevy mechanic and says there is no bulletin for it and our speed limits are max 100km/h anywhere near here so they cant even check it. Be interesting to know why though if anyone ever finds out.

I will say it sounds like its coming from passenger side front. Keep us posted.

viking59 · October 14, 2025

20 hours ago, The Hoss said:

I've had my 24 6.6 gasser for almost 2.5 years. I had the same whine at 130km/h (80mph) since new. My buddy is a Chevy mechanic and says there is no bulletin for it and our speed limits are max 100km/h anywhere near here so they cant even check it. Be interesting to know why though if anyone ever finds out.

I will say it sounds like its coming from passenger side front. Keep us posted.

Might be Right Wheel bearing / Drive Shaft.....

15DenaliSummit · December 8, 2025

So wanted to give an update on this, been back to my purchasing dealer and pretty much was told to pound sand by the shop foreman. So went to a third dealership that was recommended by a good friend and they have been the most helpful. The truck is currently there for the third round of testing and has been escalated to be investigated by an engineer in person. Dealer has done multiple tests and had to order a dedicated picoscope for the 6L90 to go back and forth with engineering to get where we are now. Hopeful something comes of this but I’ll post another update on what happens with it.

Chuck FB · December 8, 2025

5 hours ago, 15DenaliSummit said:

So wanted to give an update on this, been back to my purchasing dealer and pretty much was told to pound sand by the shop foreman. So went to a third dealership that was recommended by a good friend and they have been the most helpful. The truck is currently there for the third round of testing and has been escalated to be investigated by an engineer in person. Dealer has done multiple tests and had to order a dedicated picoscope for the 6L90 to go back and forth with engineering to get where we are now. Hopeful something comes of this but I’ll post another update on what happens with it.

Because this dealer or GM has a suspicion the noise is coming from the transmission, I was curious as to if the trans oil has been changed anywhere along the line and the oil itself evaluated for condition as well as the amount of metal on the magnets or contaminants trapped in the filter.

Of course if they pick up on something once they do this test, that would mean either dropping the pan at the very least or pulling the transmission and working on it to discover what it is or if GM just says replace the trans.

I wonder if there is a chance its a planetary set that under that speed and load could cause that whine.

Another JR · December 13, 2025

You would think that a transmission engineer, when given data about wheel rotation speed, noise frequency, and what gear the transmission is in when the noise occurs, could use the axle and transmission ratios and gear tooth counts to identify if a particular gear set tooth meshing frequency matches the noise frequency. This kind of analysis is done for helicopters, where transmission gear meshing frequency tones are a major component of cabin noise. Planetary gear sets often are the dominant noise source.

15DenaliSummit · December 15, 2025

Okay so here’s another update for you guys. Nothing happened pretty much. The engineer came out and said he didn’t hear the noise, which is absurd because you hear it every time when you get to 75-81mph under load. So they gave my truck back and said to review in 6 months. This is the third repair attempt at this dealer so a lemon law lawyer took my case and sent a demand letter to GM to force their hand in this. And Chuck, I haven’t dropped the pan and neither has the dealer. They haven’t done anything but testing. The dealer is going to try to go to bat for me and get the engineer back out and do a drive with me to hear the noise. Another JR, it’s a little strange because it does it regardless of gear, 4,5,6, and if anything it’s louder in 4 and 5.

Pryme · December 15, 2025

No speed limit past 70 in my state so I won’t know if I have a whine at 80mph.

Chuck FB · December 15, 2025

21 minutes ago, 15DenaliSummit said:

Okay so here’s another update for you guys. Nothing happened pretty much. The engineer came out and said he didn’t hear the noise, which is absurd because you hear it every time when you get to 75-81mph under load. So they gave my truck back and said to review in 6 months. This is the third repair attempt at this dealer so a lemon law lawyer took my case and sent a demand letter to GM to force their hand in this. And Chuck, I haven’t dropped the pan and neither has the dealer. They haven’t done anything but testing. The dealer is going to try to go to bat for me and get the engineer back out and do a drive with me to hear the noise. Another JR, it’s a little strange because it does it regardless of gear, 4,5,6, and if anything it’s louder in 4 and 5.

I would imagine someone familiar with how the transmission works as per the power flow and what components would be under load or not under load in those three given gears and have a better idea of where the noise may be coming from but the problem is if the symptom can't be duplicated they will not touch the transmission or anything else.

Going back many years ago and it was also a Chev but with the lovely bullet proof 4L60E ( bullet riddled actually ! ) and I was having random slipping issues at only 3000 miles and the shop foreman rode with me two different times and I could not get it to produce the issue ... until I would drive home from town and then it would do it !. Something was slipping in the trans randomly and the choices were the lock up converter, the 3-4 clutch pack or the 2-4 band and it kept on doing this randomly and at 5500 miles I got an idea, to try using 2nd gear from a stand still and that was enough torque to slip the band BAD and it smoked up the band and drum so bad I could barely limp to town again. Took the shop foreman for a drive of one block and oh ... yup now we can authorize to pull the trans and back then they went through it and rebuilt it and replaced everything that was damaged and the trans was ok then until of course it failed at some point because they are ******. What they found was a cut oring from factory assembly on the servo that applied the 2-4 band and that was also allowing a loss of line pressure and allowed the 3-4 clutch pack to slip so it was all a mess.

Put another way, your best case scenario is if they condemn your trans and install a new one, but the pains to get to that point !.

I don't suppose there is any chance that the rear diff or the transfer case is causing this noise, I could see that being the issues to eliminate. They need a roller dyno to put the truck on, that way speed limits are not an issue although tires can become bombs then.