Hi guys, I have a 2003 5.9 SLT, AWD over 100,000 miles on it and it has been running fine for the last 4 month or so I have owned it, but a few days ago it developed a nasty whirring sound from the front end, sounded as though the fan was catching, but only on overrun !. I removed the serpentine belt and checked all of th pulleys all seemed fine except the tensioner seemed a little worn so I replaced that, inspected everything and the fan shows no sign of catching.
Now I am thinking could it be something drivetrain related, perhaps the transfer case chain ?.
It makes no difference in a turn, brakes on or off, and it is not noisy when I am on the gas, but only when I let the gas off at any speed it,s like a nasty Brrrrrrrrrrrrrrrrring sound ????
I realise it is a lot to ask for a diagnosis online, but any ideas would be appreciated as I am not a mechanic and I dont have a lot of money to throw at it, also this is our only vehicle, and I feel we should not be driving it in this condition but I have little choice and I am expecting a catastrophic failure at any moment.
Thank you , Neil.

 

make a video of the sound for us please, (you would be surprised how much hearing the sound can help)

and does it make this sound when you let off the gas with the truck in park?? also where in the truck does the sound seem to be coming from??

 

Thanks for the reply, sorry but I dont have a video cam. The noise is from the the engine bay or underneath, but definatly front end, and not localised to either side, and this only happens when driving and not in park. Also noticed a slight roughness when reversing that was not present before.
Hard to explain a noise and harder to interpret through words alone I know, but definatly something spinning and catching on something, only on overrun and the sound slows as we decelerate.
Thanks again, Neil.

 

Any ballpark ideas would be appreciated, just some basic diagnostics I could perform before I blow money I dont have at the shop.
Thanks, Neil.

 

it sounds to me like its drivetrain related, you can confirm by putting the truck in neutral when it happens and shut the engine off (make sure you have plenty of room when you are doing this, big empty parking lot would be nice, since you WILL LOSE POWER STEERING AND BRAKES) and see if the noise keeps going after you shut the engine off, if it does then i would look at it being a bearing in the front differential, or one of the front hubs, if it goes away when the engine is shut off i would take the serpentine belt off and attempt to reproduce it, if its gone then it is one of the belt driven accessories on the engine, do NOT run for long w/o the serpentine belt as it controls necessary parts of your engine including power steering and your cooling fan(like i said, big empty parking lot would be great for this)

 

So does it make this sound faster with the more RPM's the engine makes, or just speed of the vehicle?

Can you place it in neutral and does any noise change?

Does it get louder or softer when you turn?

Have you checked all the fluids in the truck including differentials?

I am trying to nail it down a little bit farther from and engine issue, trans/T-case issue, differential issue, or a wheel bearing issue.

 

Sounds like a bad ujoint or loose torque converter. When something is under load aka accelerating everything is tightened by the torque of the engine but whe you let off the accelerator the slack becomes apparent and causes strange squeaks or noises. You say its in the front but it cpould possibly be in the rear end and maybe just sounds like front

 

Thank you all for taking the time to respond, I will check the things you have suggested and get back to you.

 

Well I thought I,d give an update on the problem, I checked most of what you folks suggested and narrowed it down to the drivetrain, and decided that due to limited tools and know-how I had to take it to the shop.
The front diff is shot and needs replacing. Now when I purchased this truck, the dealer assured me that it had been serviced and all of the fluids replaced etc. Well my mechanic says the front diff was completely dry !.
Though I can believe my own ignorance at believing a used car dealer, what I do find amazing is that this thing ran all of this time in that condition.All I ever heard was a very slight whine untill it gave out that I put down to high mileage.
The irony is, that my wife and I work 2 jobs so I dont get much free time, but we were taking the first week of the year off, and I was going to spend some time checking the diff's, changing oil etc. And I was going to come here for advice.
Too late.
So expensive lesson learned, and thanks to all who gave me advice.

 

sorry to hear about what happened man, but glad you finally got it figured out, yes lack of maintenance is a bitch on moving parts