Ok so I am talking about my 97 discovery SD with 123k miles. Lately i have been hearing this noise but there are some prerequisites to hear it first. Im in alaska and we have been having a cold winter. Now my truck has been sitting outside all night and were talkin about -5 - -15 degree weather. I start it up and let the engine run for about 15 mins sometimes more to get the block warm before i go to work. When i get it on the pavement and it passes 30mph i start to hear this humming sound coming from somewhere near the front. It is a weird noise and is easily heard above the music at a normal to lower level. there are no strange vibrations accompanying this and if there were it would be hard for me to tell because the roads are so bumpy and messed up from recent snow. Now here is the kicker. the same noise goes away if my truck has been parked in our garage all night whick is kept around 50 degrees. I will not hear the sound again untill my truck has been left to freeze all night. Now i cant always put her in the garage because i get off late and trying to play musical cars with the roomates at 1130 at night can be a hassle. Now originally one of my roomies and I decided the front wheel bearings were shot, so I replaced them as well as the front brake rotors and pads (had a warped disc up front but now i can tell there is a very slight warp in one of the back rotors . the old bearings and races were totally fine but i replaced them anyways. all the ball ends etc looked good and greased, the axels and hubs were well greased. Im stumped here guys and before i put more money into something its not i am asking for help. the sound almost sounds as if someone were holding a piece of cardboard against a spinning tire or something. hard to explaing. hope someone can help out.
Sincerely ,
Completly lost in the sauce

 

Have you serviced your swivels (drainable CV joints) on the front? Perhaps that would be a good place for synthetic. Same for diffs, transfer case, and the drive shaft (for the drive shaft I like the "green" synthetic grease widely sold by farm stores, some parts stores).

The swivel cavity is the size of a softball inside, there is a lot of oil / grease in there. Some use #00 grease, but in your temps????

 

Agreed, with the low temps I would use full synthetic 74-140 gear oil in those swivel ***** (and all the diffs).

 

If you park in the garage then go to work does the sound come back for the drive home after its been parked in the cold all day?
I'd look to things that don't warm up when driving, so that would elinate the drive train and engine compartment. At least for starters.
There are various plastic shields and covers that are somewhat flexible that could possibly rub at one temp and not another.

 

Might want to check those U-joints as well.. Give them some grease..

A "Frozen" U-joint will have quite a bit of turning resistance...

I don't mean frozen as in stuck..Just frozen as in damn cold..

John

 

The difference in the temps (above/below the freezing point of water) stands out to me. Do you have some condensation in your front diff and/or third member that might be freezing?

 

Front diff is not being lubricated properly for whatever reason, gear oil is to thick, water in diff are the first things I'd check.

 

everybody here has what I was gonna say. Its likely your cold fluids

 

Here's a link to a paper on various fluids, lab tested for hot and cold. http://www.oilteksolutions.com/GearLubeWhitePaper.pdf

Provides a side by side comparison, of course AMSOIL comes out on top usually. But... it does compare others with the same yard stick. Some well known brands failed, others did better than I would have expected. Thicker oils have more of an issue at very cold temps. Synthetics perform better. You are dealing with a splash lubricated system. So a synthetic 75W90 will outperform a conventional 85W140 at the -15 temperature.

I like the idea of an ice ball forming from condensation, but wouldn't that be at the bottom of the diff? If it was, and large enough, you could take out the drain plug when cold and have nothing come out. Now that would wake you up.