To be led down the merry path a 3rd time, try this: Drop the belt and run the engine for 30 seconds. If sound is gone, its possibly the tensioner or accessory (alt, ac, etc.) related. Second test is reconnect the belt and using a rubber bushing on your floor jack, raise the engine 1/4" at teh oil pan (no more or YOU will cause damage). If sound is gone its likely a motor mount casuing excessive engine vibration showing up at the belt.

__________________
Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)