Hi, I'm new here and just trying to get a feel for what's going on with my Toyota. Without the hubs locked, no vibration, no noise at any speed. With hubs locked in 2wd, there's a fairly loud, unnerving rattling noise at 40+ mph. Hubs locked in 4wd on flat pavement, it vibrates pretty heavily at 15 mph. No vibration or issues on snow or mud in 4wd, though I'm rarely over 15 mph in those situations.
It was in 4 on straight pavement due to it being very icy out. Vibration and noise seem to come from the front end.
What should I be checking, what could be the culprit?

 

It could be the CV axles

Front differential

Front drive shaft

Bad ujoint

Drive shaft out of phase

drive shaft Flange bolts replaced with the wrong ones and about to fall off

Cut boots on the CV axle allowing all the grease to escape

Get under there look for what moves where it should be tight