Your forward dial may be the tightness of the speed change line is not suitable.
What you said may be caused by the high screw/tight shift line/internal resistance of shift line. Also, it is normal to scrape the front dial with the largest chain, and make noise with the largest rear dial, because you used the incorrect speed change combination (the small belt is also small).
So you'd better go to the store to adjust it, and then you can learn from it.