Micro-Stutters?

Hi: I have been running FS2004 for a long time now...Get good frame rates, etc...Suddenly I have started getting the "micro-stutters" on landing and some turns...Can someone suggest which features to turn down to solve this? (or any other suggestions) I have defragged regularly and have not recently loaded any major add-ons...Thanks a lot...
Steve in Kansas
Steve in Kansas