can PC noise damage speakers?

You are having interference issues on your computer, it is not normal that you hear noises when scrolling down...etc.
Try to reconfigure drivers or check if there is something wrong on the hardware conf settings.

I do not know if this is the best advice for you, but whenever I have a strange computer issue that seems to not resolve itself. I will backup all of my important information, and reinstall the operating system. Having a fresh install of an OS could speed up your system and your settings will be at default. If the problem still continues you can change sound cards.

Hope this helps, and remember make at least 2 copies of your backup. Because once you loose your data it is gone.

I really doubt it.