Thanks for suggestions. It's a good thing that it doesn't rain much during summer here in sunny California. Otherwise the noise from the wiper would've driven me crazy.

I tried to move/swing the wiper to see where the noise is coming from . I noticed that the wiper arm is very strong and it has enough registance that I was afraid that I would break it if I forcefully moved it. How does the single wiper work? Can I manually move the wiper side to side without hurting it?

Thanks