I can hear a howl when on the gas coming from the rearend but could it be a outer axle bearing seeing i just built the rear diff about 3 months ago and only 400 miles ? If you let off the gas it goes away ? Axle bearings are the only ones i didn't replace !

 

Jack it up, and check things. You can save the fluid, and re-use it if its pretty clean..... turn things by hand, if it feels crunchy, theres the problem.

Did it slowly get louder? Was it there before you did the rear? Or did it just come up all at once?

 

It sounds like the pinion bearing is going bad. I had this same problem and same noise on a car many years ago.

 

Pinion bearings and seal were brand new national parts and set up correctly ! Will axle bearings make that noise or not ?

 

Any bearing can howl. Jack it up, turn things by hand. You may or may not be able to feel it. If you run the truck up on jackstands though, you should be able to localize it.

 

The car I had the pinion bearing go out on was a new 86 camaro with less than 12000 miles on it. So it doesn`t matter if its set up correctly, new parts can fail at any time, and for any reason.