strange noise.. maybe transfer case

[teriteresa]

HI...

let me give you a bit of history.. we have a 99 merc. mountineer AWD V8..

starting make the weirdest noise.. lots of road noise then a metal on metal sound..like a card in bike spokes... did for a minute then stopped and then did it constantly loud.. sounds like coming from left front tire area.. no vibration (seen that a lot on here) turning doest make a difference...
jsut the noise just gets louder as you increase speed

thought it might be hub so bought new hub assembly... but upon that realized the noise was actually coming from under..

so took it to the mechanic.. wich of course did not get to hear the noise....
but thought it might be the u joints but mechanic said those looked great BUT lets check the transfer case.. no grease so the filled that b ack up and for about 4 weeks maybe 500ish miles NOTHING then all at once noise came back... so put more grease in but it ddint stop the noise this time...

jsut wondering what it might be... any ideas would be helpful
thanks for reading!!!