well, i don't know anything about code errors and such, but i know that the most common cause of scratching noises from the HD is file fragmentation. the cure is to defragment the drive using a third part utility. My suspicians that this is is your culprit are supported by this happening while running a browser which does lots of adding and deleting of files in its cache. if this is the only place you get the problem, a quick and dirty solution might be to just clear your cache. but eventually the problem will resurface. (ok, it wil resurface if you defragment, but not as quickly)