Originally Posted by YUM360
but its drives ok without noise untill you pick up speed and then it knocks
Dave, sounds very much like it's the chain in the centre diff.
It has stretched a bit, enough to skip or jump a tooth (or two) when you acceretate. I had the same thing happen once after I replaced a cracked front diff casing with a plated one. On my Saph the chain was the next standard (weak) part to go.