Popping grinding noise while under acceleration

The vehicle was making a popping grinding noise well while under acceleration the popping noise would go away at about 45 mph. Then if we slow down and then start going again it would start popping and grinding again. We discovered that the transfer case was definitely bad. I replaced it with a re-manufactured transfer case the problem went away. About five days later I was at a stop on an uphill incline when I started to go it popped again about seven or eight times then the sound went away. Then I was able to drive it everywhere just fine until I’m back at a stop on an uphill incline and that’s when it starts popping again about seven or eight times. It is definitely the same exact feeling and noise as before, so I thought that it was weird that replacing the transfer case seem to take care of the problem, but now it’s popping again. It’s not as bad as before it’s not as frequent and it doesn’t pop for as long but it definitely is the same exact feeling and the sound as before. Could it be that the new transfer case is bad or could it be something else? The drive line seems to be fine. One of the shafts was worn down a lot from the bad transfer case barring so we replaced the shaft. So I think we can rule that out.