The Grimefighter "stub" is installed by default, a mistake, IMHO. To fix, go to Control Panel... Programs and Features and select Avast. At the top, select Change/Uninstall and in the resulting dialog, select the Change section. This will show you all of the options in Avast, even those not installed. I am sure that here you will find that Grimefighter is selected. This is not the actual Grimefighter programme (which you must purchase) but the "stub" (or whatever you call it), which checks to see if it thinks you need Grimefighter. Deselect this, and reboot when asked. The "ads" will go away...
Gregg