[client] freezing every 2 seconds in game (5.6)

i've been playing on winxp for a long time slightly above the minimum system requirements with no issues. however, since patch 5.6 i have experienced consistent freezing every few seconds. my framerate and ping are fine while i am not freezing, and nothing seems to make the freezing more or less likely (it doesn't happen more often when i have more character models on screen, or when i use a skill as opposed to standing still)

if i freeze up while i am inputting a command, the command won't go through until i stop freezing. for example, if i go to place a ward in a bush and then turn around and walk back to lane, if i freeze up while i am warding, i will ward the place i was moving back to instead of the bush when i regain control. -_-

i've tried deleting old programs, defragging, closing skype/firefox while i'm in game, playing in fullscreen instead of windowed - absolutely nothing helps. the game runs completely smoothly outside of this. i've checked task manager and my cpu usage doesn't go above 60% even during freeze-ups, so i'm likely not overloading my computer.

i've also noticed that now lolclient.exe, lolpatcher.exe, and lollauncher.exe will stay open even while the actual league of legends game is up, which is something new to this patch. however, i can force close them while i'm in game, but this does not help the freezing either.

does anyone else playing on a lower-end system have a problem like this?