axel or hub noise??

I searched and didn't find answer so i'll ask again. When in 4 wheel and only under load I get a bad poping noise from the front left axle area. The more load its under the more noise it makes, no load no noise. It almost sounds like a hub slipping in and out but it does not feel like any slipage or jerking. Can a hub make that kind of noise? I checked u joints and there are no loose joints. I put an re3.5 lift in with lower control arms so they should be ok, could a wore out upper arm make a similar sound if it was slamming back and forth? Nothing stands out visibly so hate to attempt the colorado fest like it is so will have to tear down this weekend which will probably keep me from going.