Grinding while driving

[rumbler]

I am getting a loud humming noise coming from the undercarriage when driving with my foot lightly pressing on the gas pedal just enough to maintain speed at around 35 mph.and up. It stops when I coast and it stops when I press on the gas hard. It does not happen in park or neutral.
I have been told it may be a differential problem. Are there any additives I can use?

 

[MAXIMIS1]

check your rear end for wear or if lucky fluid contamination/ or lack of

 

[rumbler]

Thanks,
I had the differential fluid level checked and it was full. The service tech said it was very dirty and thick. I had it changed and the noise is getting less each day. I was told that the new Valvoline gear oil does not need additives and has conditioning agents in it and that it may take some time to condition the gears. Any way the truck is noisy for about 10 minutes initially and then the rumbling gets less as I drive. I'd say it is 60-70% gone.

 

[rumbler]

Just an update the noise is almost gone today. I think the new fluid is really working wonders. Thanks.

 

[savagefan]

Ahhhhhhhh, happy ending!

 

[F14CRAZY]

No oil is going to condition gears

 

[rumbler]

Im not sure what it did but the differential is now quiet and I understand that the gears are a mechanical device and not pourous like wood. I am glad it worked.

 

[F14CRAZY]

But yeah it's good its fixed

 

[fixinthe92]

Thie is encouraging. I have a 92 with 4WD (Dana 35 front axle) and as I increase speed, it sounds as if it is on rumble strips on the shoulder of I-95. The rumble continues and slows down as I apply the brakes. It is really bad at 55 mph. I have replace front wheel bearings, brake pads and had the rotors turned. Does this describle the noise you had??

 

[fixinthe92]

... forgot to include that I checked the fluid level in the front axle only. Should probably do the same in the rear, huh?? Any help in identifying the source would be very helpful.