You could temporarily turn on the 'Show detailed info on performed actions' this option is off by default, this should give you an idea of what is being scanned and what might be accessing these files to cause avast to scan them.
- Standard Shield > Customize > Advanced - This function is also on the Web Shield and Internet Mail providers so you should also check those.
If you identify a common file being scanned then it could be excluded from scans, assuming it is a legitimate file and not something malicious.