First of all, I use Skype on my Macbook Pro (Mac OS X 10.7.2 Lion)
When I talk on skype with ex. 2 friends, then one of their voices become very scratchy, and I only hear some of it. When I ask my other friends in the group, then they say that they don't have the same problem.
I've tried to shift headphone, shift between headphone and computer sounds, and I've been looking all over the preferences. I've tried to reinstall Skype too. And I have the latest version of Skype. When I call Skype Test Call, it's not scratchy.