I don't have the problem you describe when I play the sims. Here are some general thoughts though.
Is this a recent problem? If it is, did you change anything on your system just before you started having it? For example, did you install any new software, upgrade any hardware, download any new objects or skins for the sims, etc.
If the answer to the above is "no" then perhaps you should uninstall the game and reload it. If you have some cool homes, neat character developments, etc. that you don't want to lose, then copy the file "game data" to another directory on your drive. After you reload the game, test it out and see if you still have the problem. If it's gone, copy your old "game data" folder back to the Maxis directory. Test again. Either your problem is solved or something is corrupted in your "game data" folder.