Rattle under 95 4runner

I have a rattle coming from the front underside of my 4Runner. It only rattles when in 2WD. In 4WD, everything is fine. I took it to Toyota today for a new muffler, and asked them to check it out. They told me that the CV joints were fine, and that the ball joints were worn. I paid for the muffler and left.
I forgot to tell them that the rattle was only when I was in 2WD. Is it possible for the ball joints to make that rattle when worn out, in 2WD and not in 4WD?

Welcome to the AF!

Maybe it's a noise associated with your ADD actuator.

You can try removing the front propellor shaft (after putting reference marks on the bolt flanges) and putting it in 4WD. Then, the only difference is in the position of the actuator and locking of the differential to the propellor shaft flange.

If the sound still dissappears when you put the transfer case in 4WD, then it is not associated with the application of power in 4WD (since the front wheels don't know you've put it in 4WD), only the position of the actuator. Then you can remove the actuator and see if there is something worn out or loose.

If removing the propellor shaft stops 4WD from eliminating the noise, then the noise is in a power-transfer component (half-shafts or propellor shaft etc) or something that is a structural part of the truck - absorbing the torque of the front wheels.