New built X5 help!

[Markoxx4]

Hi guys,

just spent the last couple of days finishing my X5, my only problem is that im not sure how tight to have the belt. it seems pretty tight but when i push the car (without motor) it souinds like the belt isnt meshing in places.
It runs smooth but it makes a bit of a 'crunching' noise like the teeth from the belt sliping into the groves on the diff or pulley near the motor has any one else had this? can it be solved or is it just part of the x5 experience!?
cheers if you can help,
Mark