It does that a bit here also on replies, but not so much on posts. On your board at
http://www.sleeperpicks.com/ , I did notice some flickering after starting to enter a name/pw on some new topics and on all replies. So, it is not wholly limited to your board. One of the programming types will have to comment on the cause.
Added: There
are animated gifs on the posting pages. If you scroll so they are not visible, the flickering stops!!