Noticed for a while my Windows 7 PC had become very sluggish, specially when playing videos. Task manager showed the main Avast process consuming CPU at a constant rate of 20 - 25 percent. Finally traced it to the Web Shield module. I have now turned that module off and the improvement in performance is very noticeable.
Bit more nuance to the issue, what is causing it are the “Enable Web Scanning” and especially “Use Intelligent Stream Scanning”. I guess it is fine on higher end performance laptops but not on my Windows 7 machine.
Turning off Webshield kills your protection when you’re on-line. Not a good idea.
How much ram does your computer have ???