iPhone 4s goes crazy

About once every 4 months my iPhone 4s goes crazy. To be more specific, little boxes like square halos appear on the screen around the perimeter of each icon. It starts speaking every word that appears on the screen. Everything is frozen so it's not possible to use the device. A hard reset doesn't work--the problem just reappears when it restarts. One time, I tried removing the sim card and that solved the problem. However, it happened again yesterday and removing the card didn't help. I ended up restoring the software, which worked but is a tedious and time consuming operation because of all the apps I have and custom setting that have to be redone. Also, I'm concerned that this could happen when I'm traveling and am not able to connect the phone to my computer. Has anyone heard of this problem? Do you have any suggestions for preventing it or fixing it, other than what I've tried? Thanks.