I've never driven an XTrail, but have tested the CRV and RAV4 cute utes, so my speculation could be perhaps this hum is the buzziness that a lot of 4 bangers have? When cold, the RAV has a bit of that moreso than the CRV...but both exhibit this buzziness to a degree. When it warms up, it's a lot smoother.
No need to call somebody insane Cp, if you read the post, Atm drove 3 DIFFERENT X-Trails to see if he/she got a lemon the first time.