Xoutpost.com - X5 noise

Hello everybody,
I'm new here and I just bought 2006 X5 with 100 k last week. When accelerating the truck is very noisy and when driving around 100k/h I could hear a wounding/ humming noise coming from the rear, like bad bearing. Is this normal? Expensive truck like that can be that noisy? I know it is not much for description but maybe any of you heard anything similar about it- please let me know – thank you in advance.