Thanks Bob,
I tried your suggestion but it hasn't changed its behavior.
It doesn't get stuck to any particular file or folder, I just can see that it takes long to perform a quick scan (I presume it should take about few minutes in my case with a 500 gb hard drive where half is still free). Otherwise the program works fine, get the latest updates, and can quickly update softwares. Its just the scan that takes too long, we have another laptop at home and is also running Avast free, it has the same problem too, and we have no issue at all with our laptops.