I have a 2009 MacBook Pro running Leopard with a 500 GB drive. I seem to be losing hard disk space for no reason while web surfing in about 500 MB chunks. I tried emptying the trash, clearing the safari cache and history, and all that returned was about 200 MB. Since I noticed this a week ago I've been keeping track, and have lost 4.5 GB of space for no reason. I'm not adding files nor running time machine or some other backup that's constantly creating a disk image. What should I do?