Sounds to me like one of the drive shaft universal joints binding when you are turning. which means its worn out, being in reverse means the joint is going backwards which would cause it to bind as well. Might be tricky to spot when the van is on a lift with the wheel off as there is no weight on the wheel assemble and on torque going through the drive shaft its self as its not turning, there would be a lot of load going through the drive shaft when driving and even more going through the universal joint when turning. Hope this might shed some light in what might be going on there