I had the same noise and it turns out to be the belt tensioners. There are two of them, one for the compressor and one on the main belt. You can test all the pulleys, one at a time, by applying a small amount of lubricating oil to them. Apply the lubricating oil one at a time and start the engine and see if the noise goes away or decreases. I have the same X with the same amount of mileage and if you have not replaced both tensioner pulleys, them that is for sure your problem.

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2010 X6 50i
2005 X5 3.Oi, Many Options
2015 HONDA CR-V EX-L
1998 ACURA 2.5TL

MODs
- Driver's outside mirror light
- Voice Recognition Module
- Blaupunkt Entertainment System
with Digital TV