90 4runner rubbing noise?

hello here' the low down. I have a 90 4runner v6 4wd. It is intermittently making a loud rubbing noise in the front right of the truck. It starts randomly and sometimes stops on its own or will start when I hit a bump,it will stop when shifted into 4wd, or when I brake or turn hard to the right. but happens only a portion of the time. took it to mech, he removed front drive shaft and said prob went away, it seemed the vacuum pump or the solenoid that activates shifting out of 4wd is defective. so he manually switched off the 4wd replaced the front shaft and voila!but on my way home the noise began again. super frustrated, 3rd mechanic in a week. any suggestions

Could be a lot of things, bad CV joint, bad bushing somewhere, plastic caps missing from the steering stops, ...
Additional details might help.