There is a vast difference between frame rate drops and "stutters".
Typically, frame rate drops are due to resource issues. This can be anything from the CPU being taken away to do other things, to your network being pinged by some torrent or other P2P software to some device running out of resources (memory, sound buffers, video card ram....).
Stutters are typically caused by the video card having to load resources which are needed immediately, but were not able to preload, for some reason.