I built an 01 suburban for a guy. It's a 4btaa, NV4500, chevyauto 4X4 T case with an exhaust brake. In the bown shift when using the brake, some times after it holds back for 20 secounds something that sounds like metal on metal lets loose and it starts to freewheel. It is a mechenical noise in the area of the bellhousing. When he pushes in the clutch it will grab again when it is released. The clutch never slips under lots of torgue. He took the trans out to replace the sincros and could not find any other problems. So he opened the T case to check it and it is all in order. So we thought it was the auto 4X4 contols so he disconnected the shift motor to keep it in the two wheel mode but it is still giving the same thing. We have come to a conclution that it is in the clutch. But to me it is stange. Please help me think strait, what are we overlooking.