What’s this hum,

[Sdude2008]

1999 3.0 5pd 4wd
Truck has developed a hum that increases with speed and stops when the gas pedal is released. It also stops when the clutch pedal is depressed. No sound when decelerating or coasting. Also at highway speeds a kind of tapping sound joins in. It also stops if I let off the gas or press the clutch pedal. I’ve been reading everything I can tonight and havent found an answer that fits. I’ve had bad wheel bearings, hubs and u joints. This doesnt fit those problems. Truck has less than 2k on new slave, master, clutch disc, pressure plate, pilot bearing and resurfaced fly wheel. I’ve replaced the trans fluid and the diff fluid as well. Its difficult to tell exactly where the sound is coming from while driving but it seems to be the right front wheel area. I removed that wheel today and everything appears in order and tight but I did find a warped rotor which I’ll replace. It seems any noise from the rotor would continue any time the wheel is spinning. I also drove in 4W hi with no change and unlocked the hubs with no change. TIA for any suggestions.

 

[franklin2]

Sounds like a transmission problem to me. Get under the truck and check the rear motor mount under the transmission/transfer case. Make sure the transfer case and the transmission are not hitting the underside of the truck somewhere.

 

[Sdude2008]

Thanks checked trans seems to have good clearance.
Found a leaky diff cover retorqued and topped off no change. Did notice hum/tap goes away when turning to the right on the highway. Will change that warped rotor asap. Not sure how that would produce these noises but who knows. Update to follow. Thanks franklin2.

 

[Sdude2008]

Ran the truck up on jack stands and it’s definitely the diff. Looking up common failures. This is a new one for me.

 

[Sdude2008]

Found the clunk.

 

[pjtoledo]

ouch, how the hell did a 3.0 get enough power to do that?

 

[Sdude2008]

I was wondering the same. I did some reading and see it’s possible if the back tires are spinning and suddenly catch. Although I wasn’t doing any burnouts there were a few times where that did occur on wet and snowy roads. But yeah in 45 years of working on cars this is a first for me. The silver lining is I found a 3L73 on fb market which is just about swapped.