New
#11
Just double checking, how much RAM do you have installed on this computer, and how much of it is being used? If you only have a two or three gigabytes, the memory manager may be storing less active applications in the hard drive, and then summoning them back when you start to use them. If this is the case, getting some more memory would be a good idea. I would also recommend running a memtest to see if all the RAM is working, although it probably is, since you didn't mention any blue screens.
Otherwise, it sounds as if AVG is doing some sort of scan on your computer. Defragmenting your computer could help with access time (by putting things in the same place).
One last thing. How big is your hard drive? It may be worth it to simply clone your old drive onto a faster one, which will reduce the % time the drive is active, if this behavior isn't the work of software.