Grinding When Put In 4x4

[TireSmokinCamaro]

Hello, I have a 1994 Mazda b4000, and I've replaced about every single thing on this truck from the engine to transmission, to radiator and alot of smaller things. But the problem I'm having is that when I put it into 4x4 (which works good) it makes a grinding noise from the front end. This noise is persistent with the speed of truck. A mechanic has told me the front diff needs to be replaced which at first I believed cause I previously hit front diff on a rock and it now leaks cause from what another mechanic has told me, I knocked a seal outta place but he told me it doesn't leak to the point where it starves it of oil so its nothing that serious.

Looking through a manual for my truck the other day and the problem im having is right in there. A grinding noise thats persistent to the speed of the truck. So, the manual says its the universal joints..and in my case it would be the passenger side because I replaced only the driver side some time ago. (the old one fell to pieces when it was taken out).

So what I'm really asking is, could it be my universal joint or is it my front diff?
Also, not sure if it matters but all my 4x4 is stock other then the fact that I've replaced some work out parts with new parts. Its also a 5 speed manual if that matters.

 

[Raw16057]

I used to have the same problem with my 94 b4000 and the universals are the problem. when i pulled mine there was nothing in the caps but rust. change both axles and the noise will go away.

 

[TireSmokinCamaro]

Yeah, after getting underneath the truck and spinning the universal joints by hand it turns out the suspected bad joint is making a grinding sound. I'm going to take it apart and put in a new one. Thanks for the help.