I noticed that AVAST is scanning files from Facebook & my Google Mail rigorously, and causing it to freeze for several minutes, and it happens very often.
I’ve installed almost the same set of applications and AVAST on a desktop (2GHz & 2GB RAM) and a netbook (1GB RAM). Amazingly, the netbook seems to more smoothly than the desktop.
A lot depends on your settings and the providers you have running.
Have you “played” around with them to see if it makes a difference?
Disable one provider (or change it settings) at a time and see what is causing the “freezing”
Let us also know the exact version of avast you are using, and what OS.