SpywareBlaster is a passive immunizing tool which doesn't run in the background, you download its updates and apply the updates to your browsers, etc. (single click action) and you then close the program.
S&D isn't resident unless you select the option to run TeaTimer, it doesn't conflict with avast, unless it happens to take a dislike to ashDisp.exe the avast system tray icon.
So neither of those should have this effect, unless you were running a scan with S&D ?
The avast icon only rotates when it is scanning, so are you running anything in the background, like a P2P application, etc. ?
As a temporary measure you can enable this from the avast on-access protection control screen (right click the avast icon) - Standard Shield > Customize > Advanced - 'Show detailed info on performed actions' this option is normally off by default or it would drive you bonkers. This will show what is being scanned, which may give you an idea of what program is responsible for the activity, which is causing avast to scan files.
This function is also on the Web Shield and Internet Mail providers so you could also check those, if the Standard Shield doesn't show the activity (but that probably won't be required).