Weird Noise from Belts
 

Would anyone know what this noise is and where it would be coming from? Engine is the '07 X5 4.8i N62. I just replaced both the coolant thermostat and water pump so they can be ruled out. I'm thinking maybe the alternator pulley is making this noise? (Youtube link is the video I have taken of the noise)
https://youtu.be/8zeD5pMKJlY