Hi @kaiben,
Thanks for the video! that helps a lot.
I notice that you are moving across the string diagonally. This is part of what is causing the “scratchy” zipper noise. Try to move more perpendicular and it will help a lot.
the other thing I see is that once you gain confidence to strum more quickly, it will also help. This will come with practice.
Your pick angle is a bit straight. this is not generating the scratch, but is probably holding you back from strumming confidently. You will want to angle the pick a little more so it can move across the strings without catching as hard. this will help you to hold the pick in place and it won’t spin quite so easily in your fingers.
Take a look at the some of the comments from this thread, both above and below my linked comment. Richard has a nice diagram. Getting the angles figured out is what will get you moving along and strumming with confidence.