For me, too, Mouse. I've tried the Exos and Atmos packs; they've reduced the zig-zag effect by half or more, but I can still feel it trying to argue with my directional choices. I always revert back to an internal frame. (Current favorites: Osprey Kestrel 48 or Deuter ACT Zero 50+15, with a very slight edge to the Osprey. This week.)