I have been having this problem with my XC90 (2007 4.4L V8) for sometime now and the dealer can not find the problem. They tell me its the tires making the whine, but the tires are new with only 3k on all the wheels.

It only happens at 55 miles per hour and a I notice if I manually down shift to 5th gear it completely goes away.

The Whine starts softly at 50 and increases in sound right to 55 then disappears around 60.

Its something I could prob live with due to the fact that I have dealt with it this long, but it is a 50 thousand dollar car.... it should be right.

Let me know if you have any thoughts or ideas.