Humming noise

[Diezel]

I just noticed a slight humming noise when accelerating and when I step off the gas it dulls out. I did some research and saw that the front diff could be the issue so I drained it and nothing but shavings and some chucks came out so I replaced the whole this and still have the noise. Checked the front hubs and they’re fine. I ruled out boost leak because as I was slowing down I shifted into neutral and reved it up a few times and couldn’t hear anything. So it’s drive line related. Anyone ever have this issue? I’m beginning to think U joints Somewhere

 

[KyleC4]

Could be a u joint issue. I’ve even seen center support bearings make a noise like this if 2 piece driveline. Could also be rear pinion bearings As the load changes from drive side to coast side. Put the rear axle on jack stands with wheels off ground and see if you can get noise to happen. Then have a buddy crawl under there and isolate where it’s coming from

 

[2004LB7]

in 4wd or 2wd? front drive shaft shouldn't be turning in 2wd. maybe one of your CV axles.

 

[JoshH]

Have you checked the rear axle? The front isn't doing much when you're in 2wd, so any gear noise you are hearing is likely coming from the back.

 

[Diezel]

I’m beginning to suspect the rear end, I have ruled out almost everything else. Front diff, transfer case. Wheel bearings. List goes on. I’ll have to crack the cover on the rear to check but zero play in the yoke when trying to check for play in the outer pinion bearing. I did have a pinion bearing begin to fail in my last truck but the noise was only noticeable Only when coasting, the opposite of what’s happening now. But I’m run the truck with the rear on stands and see if I can’t find anything.

 

[Diezel]

I also read of someone having a similar issue and it turned out to be his FPR. Does this sound like right? My truck does have a surge at idle but kept putting it off

 

[NevadaLLY]

I also read of someone having a similar issue and it turned out to be his FPR. Does this sound like right? My truck does have a surge at idle but kept putting it off

Ever figure this out?

 

[Diezel]

Ever figure this out?

Yeah popped the rear diff cover and instantly saw it. Pinion shims are wrong and gears have a horrible contact pattern so they hum and whine

 

[NevadaLLY]

Yeah popped the rear diff cover and instantly saw it. Pinion shims are wrong and gears have a horrible contact pattern so they hum and whine

Shims were wrong as in recently serviced?? or worn out? Reason I ask, I just started to notice a light humming which seams to be coming from the rear. Wanted to see what others ran into. Diff has never been touched other than the service interval fluid change.

 

[Diezel]

Shims were wrong as in recently serviced?? or worn out? Reason I ask, I just started to notice a light humming which seams to be coming from the rear. Wanted to see what others ran into. Diff has never been touched other than the service interval fluid change.

The rear end isn’t the factory one. I replaced it when I swapped my truck from a dually to a single. So somebody may have rebuilt it and didn’t do it correctly but I don’t know. Ive been running it and it’s been fine it’s just the contact pattern on the gears aren’t the greatest so they hum.