I just replaced the front end on my 2000 Grand Cherokee with Quadradrive for the second time(both used). The first time, the front didn't lock ever which was why i changed it in the first place, so much for used parts. At least it didn't cost me any more and I didn't get a core charge either time. This one seems to lock, but I now have a whining/grinding noise from the front on acceleration that gets louder as you go faster. The driveshaft is the same, so I don't see that as an issue. Any idea what would cause that? I thought if it was a bearing in the front end, it would make the noise all the time, not just accelerating. Could it be the gears(I hope not). Is there an effective way to isolate where the noise is coming from? At least I'm getting faster at changing the front end out.

 

My son had a similar issue happen to him and it was the double cardan joint in the front drive shaft. As a test, remove the shaft and go for a test drive. If the noise disappears, you've found the problem.