If you have the rear of the truck jacked up and turn a tire by hand, should the differential make much noise? I hear sounds in mine when I do this, nothing terrible, I assume its just the sound of the gears.

However, while driving I hear a sound I can't tell where it's coming from, it's almost like a thump that increases in speed as the truck speeds up. It cannot be heard at high speeds due to road noise. At low speeds (5-10 mph) I can hear and sort of feel it. It can't really be heard from outside the vehicle, only inside with windows up.

I could not duplicate the sound with the rear end off the ground, I was turning the wheels/drive shaft by hand today trying to recreate the sound, nothing...

 

This is just an idea (wishful thinking), could be way off...

Has anyone ever heard of the speedo cable making noise where it goes into the tranny? I know it needs lube, it squeals and my needle bounces.

Would be a pleasant surprise, not having diff/bearing/ujoint troubles. Sound possible?

 

Anything stuck in your tire?

 

Check your pinion shaft for proper preload or for play. Somtimes you can have a lot of clearance in the pinion bearings and the pinion shaft will actaully scrape on the carrier housing inside the diff. I had this simular noise in my truck for several years before I found the marks on the carrier and put two and two together. It had actually worn grooves into the housing!!! No other symtoms really. Just the noise believe it or not.

 

Nothing stuck in the tires, doesn't sound like the rocks my M/Ts pick up anyway.

The rear end play seems the same as it's been since I got the truck, not a whole lot, but there is some rotational play.

Here is something interesting I found tonight. While coasting through a parking lot, maybe 5mph or so and listening to this sound, I decided to pull the e-brake (it doesn't have much stopping power) and see if it had an affect on the noise. It stopped until I released the brake. I suppose when I have the time I may pull the drums and have a look.