"Purring" noise while coasting

[jcmott]

"Purring" noise while coasting at medium speed. The noise is like a surging, muffled rattle. It sounds like a giant cat under my truck. The type of noise is similar to the harmonics of a bearing that is shot, running smooth for a second and then rattling for a second. The amplitude of the sound is such that it's difficult to hear if I have the radio on. But it's quite noticeable with the a/c and radio off, windows up.

I am the new owner of a 2016 Ram 2500, 4x4, 6.7L Cummins, 68RFE, with about 125k miles on it. I need to know if this sound is normal or if there's a problem with my transmission.

This sound occurs when I let all the way off the throttle at a speed range of about 45mph down to about 25mph. It may happen at higher speeds, too, but I just can't hear it. It will purr until the transmission releases (stops holding back the truck) at a speed of about 15-20mph.

If I shift into neutral, the sound goes away immediately, so it seems to be related to the transmission, not engine, drive shafts, diffs, wheels, etc. If I give it just the slightest amount of throttle, the sound goes away.

The exhaust brake is off. (The exhaust brake works fine.)

The sound is louder when the transmission is cold (not at full temp) and gets quieter at full temp (150F-160F).

I typically notice it while in trans gears 5 Lock and 4 Lock.

The sound seems to not be related to the engine at all.

It doesn't produce any vibration, as far as I can tell. It's just a noise.

Everything else works just fine.

 

[GTyankee]

You could go to a REAL a transmission shop & have them drive it

You ought to be able to find out where all the 4X4 people take their vehicles to get them fixed or to have upgrades done

The way that you explained it, it could be your differential as well

 

[jcmott]

Thanks GT. I changed the oil in both diffs. The rear was just a little dark, but didn't look bad. Minimal metal shavings. The front had water in it. Milky oil with water at the bottom. I cleaned it out, put new oil in, and repositioned the vent tube away from the wheel well. I also put a cap over the vent to protect it from spray. The noise is still there. Maybe the gears are worn from the water?? Or maybe it's something else.

 

[zcapogna]

Jcmott, you ever figure out cause? I also have 2016 with 120K and same exact problem.

 

[RamDiver]

jcmott hasn't been online since October 2022.

Hopefully, he'll respond if he receives a reply notification.
.

 

[zcapogna]

"Purring" noise while coasting at medium speed. The noise is like a surging, muffled rattle. It sounds like a giant cat under my truck. The type of noise is similar to the harmonics of a bearing that is shot, running smooth for a second and then rattling for a second. The amplitude of the sound is such that it's difficult to hear if I have the radio on. But it's quite noticeable with the a/c and radio off, windows up.

I am the new owner of a 2016 Ram 2500, 4x4, 6.7L Cummins, 68RFE, with about 125k miles on it. I need to know if this sound is normal or if there's a problem with my transmission.

This sound occurs when I let all the way off the throttle at a speed range of about 45mph down to about 25mph. It may happen at higher speeds, too, but I just can't hear it. It will purr until the transmission releases (stops holding back the truck) at a speed of about 15-20mph.

If I shift into neutral, the sound goes away immediately, so it seems to be related to the transmission, not engine, drive shafts, diffs, wheels, etc. If I give it just the slightest amount of throttle, the sound goes away.

The exhaust brake is off. (The exhaust brake works fine.)

The sound is louder when the transmission is cold (not at full temp) and gets quieter at full temp (150F-160F).

I typically notice it while in trans gears 5 Lock and 4 Lock.

The sound seems to not be related to the engine at all.

It doesn't produce any vibration, as far as I can tell. It's just a noise.

Everything else works just fine.

jcmott, so I finally turned my RAM in for repair. I had a number of broke exhaust mani bolts and (for now) this got rid of my tranny noises. Sounds silly but I think we were hearing engine noises coinciding with down shifting...or whatever. In any case, its been months and the noise is gone. Check the exhaust mani bolts if still having noise.

 

[jcmott]

Thanks for the tip, Z. I'll keep that in mind. I haven't figured out anything else with it yet. But it isn't getting any worse, so I've just kept driving it.

 

[mcenz25]

I'm glad I found this post. My '14 2500 6.4l does the same thing. Recently, with the colder weather, a cold engine exhaust leak has developed.

It seems like the tranny is trying to get to the lowest rpm it can manage in 6th gear. One mechanic told me this is normal and that I should hit the tow/haul switch.

 

[zcapogna]

Exhaust manifold broken bolts. I've had a few vehicles have this problem. And when it's cold, the metal shrinks and the exhaust leak develops. In our cases, there was also some noise. Goes away when it warms up, the metal increases in size a little, and seals the leak. A trip to a mechanic for an inspection of exhaust manifold bolts should do the trick. Really don't want to sit in idle with an exhaust leak at the manifold since the fumes could leak into cabin