Humming and clunking sound from under my truck PLEASE HELP

[Heavychev]

I have a 1998 Chevy k1500 5.7L which is on its second engine and transmission. I bought it used with the intention of fixing it up with my dad, upon reaching the finish line with the project I started to daily the truck. It was running and driving great for the better part of this past month when suddenly an inconsistent humming and clunking started to occur. The trucks runs without issue until everything is up to temp or until I really start to push some speed. The humming isn’t noticeable until I’m slowing down and then it’s loud and grows even louder when slowing down its then followed by a very loud clunk and it’s back to normal. Mind you the transmission isn’t new it was bought from a wrecker yard with 180,000 kms on it (4L60E). I threw that in, aswell as a new rear end because the last one went. But like I said it drove fine for the better part of this past month and the fluid is fine, the truck shifts alright too. 4 wheel drive activates and deactivates with the press of a button no problem. I’ve exhausted the extent of my research with the matter and despite having a small amount of knowledge with older Chevys I’m kind of stumped. I hope someone can offer some sort of advice or if any one else has experienced this and knows a fix.

[Brian Lindsey]

sounds like bearing in rear diff making noise, you said rear diff is new , or is it new to you , when mine went out it was howling loud, out of 6 bearing in rear end 4 were bad, as ring and pinion worn till teeth were sharp