Went to the snow the other day in my 2001 Silverado 1500 4x4 and engaged the electric 4x4. All was good for most of the day but then a rough grinding noise developed around 20+mph and increased in intensity with speed. Noise is not present in 2H at any speed. Hubs along with axles are around 6 months old, oil good in tx case along with differential. No looseness on drive shaft or oil leaking. So I'm lost to what could be the problem, any help would be appreciated. Thanks

 

i have an 2005 silverado it seems to be slipping out of gear but when i switch it into four wheel drive then back to two wheel drive its works fine for a little while any ideas