I have a 99 F150 Lariat 4x4 with a 5.4L, I have already changed both front hubs, the engage and disengage hub locking solenoids but continue to get a horrendous noise over 20 coming from under the truck. I was thinking it might be the transfer case but can't tell. The actuator engages and disengages, the front drive shaft only turns while in 4x4 but both CV Axles (half shafts) turn at all times.

I checked the voltage at both solenoids and both have voltage, I only noticed suction at the vacuum lines, no blowing for the disengage

Need some help with this one....