On my system I wouldn't notice a 1-4 second lock-up but it can be that avast is waiting for an essential service to load, commonly something is locking/hanging the RPC service.
During this time do you see a red circle with a bar (like a no entry sign) over the avast icon in the system tray ?
If so the current beta version of avast has a fast start (or faster) function that might help see
http://forum.avast.com/index.php?topic=27439.0 if you aren't averse to using a beta trial. Read the topic and see what snags or issues there are (they are very few) and might they effect your system.
Or you could simply revert to the Uninstall, reboot and install, this has on occasion cleared the high CPU issue. It would probably be best to download the latest version of avast and save it to your HDD, somewhere you can find it again. Use that when you reinstall.