Does the belt not run smoothly or do you hear something because the belt is out of centre?
It is recommended to lubricate the surface under the running belt with the supplied lubricant every 1 to 2 months or after every 50 kilometers. Check this in your manual.
During the first few weeks of using the treadmill, you may need to re-center the running belt. This is possible if, for example, you push off more with your left foot than your right. You must also center the belt after lubrication of the tread. Check this in your manual.