Transfer case. I sent you a pm :thumbup:

Thanks I was sorta guessing that... :( but i'd rather go in with a possible outcome than clueless..

I just had my tranny rebuilt, it was throwing TC codes, the shop said the valve body was bad too...............$4450 later, just got her back today ,running like a champ.............

I think i am getting the same exact thing!! Like At a certain acceleration and usually slower speeds its like a Grinding ish noise mixed with a wrooooing noise like

GWgwgwgwwowoooooowoo

nice description of the sounds.. :)... yeah mine has become more often now.. started when it got cold in Dec. here in Tx.. first I had some kind of light grinding noise when i would slow down and make a right hand turn. reminded me of my nitro R/C when they have gear box issue and stripped cv spline.. Then i started noticing at hwy speed between 50-80, i'd feel a vibration/shudder almost like a flat tire or wheel balance issue but not directly in the steering as you would feel with either of those senarios.. this was more on floor board and seemed like mostly passenger side. now i'm noticing it at lots of different speed but more related to higher rpm ranges.. seems to be different depending up weather conditions here in TX we are in time of year its hot or cold day by day hour by hour... I've only had my X5 since this past Aug. 2012.. 2005 x5 had 65k when i bought it .. now ive got about 74k.. had trans fulid change done at 71k. wanting to be proactive and now this.. nail bitter possible $$ to fix prob make me sick to my stomach since ive not had vehcile even a year yet..

It may be something in the x drive, i also kinda failed to think that it MAY be my driveshaft..