Ubuntu :: Constant HD Activity Bogging Down?

I'm using Lucid on a laptop, (details in sig). Often after I've been running Ubuntu for a while, like a few hours, my HD activity light will come on and not stop, causing my machine to become laggy. (A link might open 3-5 seconds I click on it, typing appears a second after I press the key, a window or dropdown menu might take 5-10 seconds to be drawn.) I currently have Firefox with one tab and a Nautilus window open. Conky says the CPU is running at 10-20%, RAM is almost all used, (I assume Firefox's cache is filling up, since I've been surfing for a while), and swap is around 25% full. I just turned Compiz & Emerald off, but the HD is still spinning away. At this point, I usually log out and in again, or reboot. I though slowing performance with usage, resource-hogging background processes and constant rebooting were Windoze traits! What gives?Apparently, this is caused by Update Manager. Unbeknownst to me, Update Manager was waiting for me to give it the go-ahead, but while it's open, instead of patiently waiting, it renders my computer unusably slow, even though it's not supposed to be doing anything.