I don't understand this either as this doesn't happen on my system, but I don't have a floppy drive.
I don't know what is accessing the floppy drive, but that is what is likely to cause the avast activity.
Now these two are classed as removable media and are loosely connected and they also share the same area in your File System Shield, Expert Settings, Scan when attaching, see image.
You can see if unchecking the arrowed option stops the avast activity, but I rather doubt it will stop the floppy drive being accessed, I really haven't a clue why this might be happening, but avast responds to activity, it doesn't initiate it.
Have you made any changes to your avast settings ?