Framerate issue with the new client

I have never had this issue with any of the other clients, but with the newest client (the 'release candidate') I get a higher framerate than I used to, but it 'hiccups', basically freezing for a fraction of a second every couple of seconds, resulting in very choppy movement. It even does it if I'm standing still with nothing around me! Smooth-freeze-smooth-freeze, etc. It drives me crazy and I can't figure out how to fix it... I disabled voice, music, video, turned the graphics settings all the way down, tried various window sizes, fullscreen, etc....nothing had any effect on it. Help!

Mine works fine except for an occassional freeze when spinning the camera around.......for about 5 seconds. That freezing used to be almost every time I spun my camera so I see that as an improvement over the last client. Also I don't crash anymore when flying. So, overall, I would say this client is better......for me at least.