Whining noise while coasting

[Zachram2021]

I’ve seen this discussed in a few other threads but wanted to get some new opinions…

I’ve got a 2021 2500 with the 6.4 8 speed trans and approximately 70,000 miles. I’ve been experiencing a faint whining noise on my drive to work which is mostly 55 mph the entire way. The noise begins after letting off the gas and coasting around 55 mph. The noise stops as soon as I start to accelerate and I really only notice it in the 50-60mph range. Noise occurs in gears 6,7,8. It’s hard to say if its coming from the rear end or not. At first I thought it sounded like a wheel bearing going out. I cannot feel the whining noise in the steering wheel or pedal, I can only hear it.

Is there any chance that this could be related to the differential fluid? The truck has towed a 23’ bay boat from Tennessee to Gulf Shores, Alabama probably 10 times but other than that there has been no towing and mostly highway commute miles. The truck has not yet had the differential fluid changed and according to the manual it was due to be done at 60,000 miles

 

[RodeoRam]

Check the pinion gear on the rear diff. I had the same whine when coasting on my 2001 1500, but I didn't know if it was the rear end or a rear wheel bearing. Then, one day I came to a stop at a red light and a blue cloud of smoke passed the cab. Luckily, I could see the Aamco that did my trans/diff/transfer case scheduled maintenance. Once I parked in the parking lot, I looked underneath the rear diff, and diff oil was pouring out the pinion seal.

I got really lucky. If you catch it now, you can avoid breaking down in BFE.

 

[ppine]

Yes. Start by changing your diff fluid and any others that are original to the truck.
My girl's Jeep starting doing the same thing around 80k miles. New differential fluid made it quiet.

 

[Zachram2021]

Just checked the diff fluid in the front and rear. The front fluid was about 1/4” below the fill hole which seems normal and the magnetic plug was clean, no metal or sludge. The rear diff was about 1” - 1 1/4” below the fill hole and the magnetic plug had some gray sludge on it and very few fine metal shavings but nothing more than I would have expected. I’m not concerned with what I saw on the plug but I am concerned with the fluid level. I inspected both axles and didn’t see any signs of leakage. Everything looks brand new. I have 10 quarts of Amsoil Extreme Gear 75W90 coming in the mail but I need to drive to work tomorrow so I’m going to top it off with whatever 75W85-90 I can find at the local parts store. I’m hopeful that changing the fluid will quiet that noise.

 

[stevenP]

There was a TSB from some time ago my wife found on some HDs that left the factory with lower fluid levels in the diffs. Mine is a 2022, and it only had 8k miles at the time.... I found both mine were low enough, I ended using 4 bottles or so to bring them both up to about an inch below the fill hole. They were low!

 

[Zachram2021]

Changed the fluid this evening. Got about 3 quarts out of it and put 4 back in. The fluid was very dark and stunk like hell. Surprisingly no metal serious metal shavings. Hopefully I caught this before it got bad.