I got the same grinding noise after my lift. Actually it wasn't so bad before I got alignment, but now I even get bad vibration in my floor. It kicks in after I reach 40mph and its either when I accelerate or let go of gas. I noticed it's happening only around certain rpms - or maybe it's my imagination trying to put one and one togheter?
I took a mechanic for a drive the other night, and he suspects drive shaft rubbing somewhere. I was thinking I had a broken motor mount after my last off road adventures, when I tried to see if VX can balance on its nose LOL
I have an appointment with Isuzu service, so hopefully I'll get a few answers. What I think though, maybe 3" lift is too much. I have 912 OME springs and 1" coil spacers. Maybe there is problem with CV angle?
I doubt it's differential - I just got it serviced, and it was absolutely fine...
I'll keep you posted on what dealer said.