Loud humming noise when I back up. Usually only in the mornings

[falkonj5]

My truck has been making this loud humming/rubbing noise from the driveshaft area when I back up. It is usually only in the mornings. Its been doing it now for about 6months. It only does it in reverse and only the first drive of the day. The truck is an 05 Dodge 4x4 automatic.
Ive been told it is the transmission fluid viscosity being different when its cold(the transmission fluid). I have been told to place the truck in neutral with the parking brake on for a few minutes prior to backing up as this will warm the transmission fluid. Ive tried this and it seems to help but not completely. The truck has 160,000miles and never had transmission serviced. Fluid is topped off and still clean. Any ideas and/or recommendations?

 

[herm0016]

Is it a 4x4? may check the transfer case fluid as well.

 

[falkonj5]

Yes it's 4x4.

 

[deadlyapp]

I came to suggest transfer case also. Had an AWD car that made lots of noise and it's because someone had used the wrong oil in the TC at some point. IIRC the transfer case should get gear oil which is very heavy.

 

[falkonj5]

well I changed out the oil in the transfer case, it was a little low but I still have the humming noise when I back up. It doesnt do it right away. It does it after i back up about 15ft. It will hum like rubbing noises for only about 2sec. Also does it some when i go forward but all this is only in the morning or the first drive of the day. Still the same as before. Any suggestions? truck runs fine otherwise and no CEL is on.

 

[LTC8K6]

Maybe try to pinpoint where it's coming from? Get someone to listen and see if they can at least ID the general area.

Have you checked the fluid level in the diffs?

 

[falkonj5]

Maybe try to pinpoint where it's coming from? Get someone to listen and see if they can at least ID the general area.

Have you checked the fluid level in the diffs?

Yes. Fluid in differentials is good.