Picture jerk!

Well I might be describing myself but this is irritating. Just recently I have started getting jerky pictures. I'm not aware of changing any settings but in desperation restored a disk image taken a month ago when there wasn't a problem; and the stuttering reappeared. Obviously it occurs when using the hat in spot mode but also in cockpit mode. Usually the stutter is accompanied by disk activity as if the program is waiting for more scenery.Frame rates can be in the 50's when this happens. It also occurs with display settings at minimum using default scenery.I am experienced with computers but less so with the intricacies of FS settings. It almost sounds like a hardware problem but where to start?FS 9.1 resides on its own XP SP2 bootable and defragged SCSI drive, an AMD 3000XP processor, 1gb RAM and a Radeon 9800XT.I would be grateful for any input; even a direction to a more relevant forum if this is the wrong place for such a post!RegardsChris