Background Noise,
It could be a number of things, but there are a couple of things you can try straight away:
1. Check how much free space you have left on your hard drive. Ideally, you need around 4-5Gb of free space for OS X to work properly. Any less than this and there isn't enough room for virtual memory.
2. Have you repaired your permissions? Go to Applications>Utilities and open Disk Utility. Select the top disk in the column on the left hand side and select "Repair Disk Permissions". This is something you ought to do every few months, but especially when new software has been installed.
Applemacster.