SOLVED! Drive train hum under load

[Ilikemy3s]

Searched the forums but did not see any about this, but may have missed it. 05 TB LT w/ 200k miles. Once warmed up and around 1200 RPMs or higher, I hear a hum from the drive train. But only under load. If i take my foot off the gas and the RPMs start to drop even a little bit, the hum goes away. i could coast down an incline and no hum. As soon as I give it gas, the hum is back. Consistent hum. And it is noticeable even with the windows open or closed and radio on. But it is not extremely loud. But my wife did notice as well. Pretty much it sounds like it is coming from the back end, but I know how sound can travel. Have always kept up on maintenece and fluid changes and truck runs fine. I just have a feeling something is going to go. Anyone else experience this.

 

[wstuckey1]

Not the power steering pump whining is it? Probably worth the thirty seconds to pull the cap and check fluid level.

 

[Ilikemy3s]

Better not be as I just as the pump and all 3 lines replace within the past 2 years. But I will check.

 

[Maverick6587]

Does this happen while in Park or only while driving?

 

[Blckshdw]

What happens if you shift into neutral when on the gas, during the hum? Does it stay, or go away?

 

[gmcman]

Have you checked the rear differential fluid? Remove the plug on the rear cover and see if you can touch the fluid.

Could possibly be a pinion bearing if fluid has been low.

 

[budwich]

If its a "moving sound" as opposed to an "engine sound", the best place to check is the front hubs..... "droning"

 

[Ilikemy3s]

Does this happen while in Park or only while driving?

Only while driving

Not the power steering pump whining is it? Probably worth the thirty seconds to pull the cap and check fluid level.

fluid was correct level and color

What happens if you shift into neutral when on the gas, during the hum? Does it stay, or go away?

did not try that .. next time i am on a downgrade and the truck is moving I will try it

Have you checked the rear differential fluid? Remove the plug on the rear cover and see if you can touch the fluid.

Could possibly be a pinion bearing if fluid has been low.

Hmm good idea .. will check

 

[Maverick6587]

I would also check and probably change your transfer case fluid. I would bet money it's what is making your hum noise.

 

[Ilikemy3s]

Noise is still there. Took the TB to a shop I have trusted for years to do things I cant or don't have time. They take truck for test drive and sure enough they hear it very noticeably They put is on the lift to locate the source.. start, put in gear, give it gas and no hum. They drain and pull cover and check seals and bearings ... they all seem fine and no metal particals in the fluid. I ask them to do the same for the front axle .. same thing as all seems fine and no metal. . . So i figure while it is on the rack, I tell them to also service the transfer case and the trans since all 4 are just over 60k miles last fluid changes. The noise is very less noticeable but still there. I guess we will see.

 

[Maverick6587]

Run it for 250-500 miles and change the transfer case fluid again. Make sure you use the Auto Trak II fluid though. Do you know what fluid they used in your diffs and transfer case?

 

[Ilikemy3s]

Run it for 250-500 miles and change the transfer case fluid again. Make sure you use the Auto Trak II fluid though. Do you know what fluid they used in your diffs and transfer case?

this shop knows me and my truck fo rhte 5 years I have had it as well as before that. I know 75w/90 was called for the diffs and the case is to be AutoTrack II but your right. I will wait the couple hundred miles and change again. Will keep you posted DO you recommend a certain brand in each ?

 

[Maverick6587]

I use either ACDelco or Mobile 1 75-90 for the diffs. I'm sure any good name brand will do for the 75-90 gear oil. Only ACDelco Auto Trak II should be used in the transfer case though. Sometimes the Auto Trak II fluid is cheaper at the dealership than it is online.

 

[Ilikemy3s]

Since New jersey is in Stay at Home, I took the TB to a recommended local shop. They test drove the truck and did some other checking and determined it was the bearings, but in pulling the cover, found the internal gears were also worn and that they were contributing to the issue. The mechanic let me know it would be more cost and time effective to replace the rear with a low mileage salvage unit. So a little over $700 later (and a 6 month warranty) she is riding nice and quiet.