Sorry if this has been asked but cannot find it. Once n a while the 738 is at altitude following Fmc path and begins flying to right then back to the left as if it is searching for the next waypoint. It eventually gets there but see saws back an d forth so much it takes double the time. Happened at 340 alt ith 30000 lbs fuel. Tried lowering alt and speed (.77M) but still happens, Thanks