Actually everyone in here is likely wrong, I've been through this before
its actually a common exploit/hack that has been popular in the past
recent months.
Your website is STILL infected, even though you aren't experiencing anymore.
Here's what happens, the 301 redirect only happens once or twice, then you
won't experience it again. It will happen ONLY when a user visits your website
from Google, thus making it hard for Webmasters to know whats happening.
Your site has a sneaky redirect happening, I wrote a post about it around 4 or
so months ago. Check your websites code, as it will still be visible. I found the code
in the footer of my site, but it might vary. Sometimes the code is encrypted, other
times its a visible php redirect. If you want give me your URL and I'll see if I can
find it on your site.
Again, your site is still infected, even though you think you fixed the problem.