Clicking noise while using 4wd
 

I have a 2000 F250 4x4 and while using the 4x4 there is a clicking noise coming from the front end. I have replaced both of the factory auto/maual hubs with aftermarket loickout only but that did not fix my problem. Only seems to make the noise when under power (spinning) not while driving in 2wd mode with hubs locked in. Seems both wheels are trying to grab but is noisy. has on the fly knob not manual 4x4 on floor. Thanks in advance