08 250 Power stroke issue
 

A friend of mind has an 08 250 4x4 Had it at the dealer for 4 weeks now and can't find the problem. The problem is when in 4 wheel drive he heres a wineing noise. On a lift the noise goes away. The dealer has replaced many parts on it and can't find the problem. Has anyone had this problem or have any ideas what it could be. I told him maybe it's a shorted wire. The dealer is also looking for an answer. Many thanks in advance.

possibly a hub? or low on oil in the transfer case? that is quite odd though