Sometimes a chain that is too loose will cause this because the chain comes out of the groove on the guide bar and the angle of the teeth push it or pull it one direction or the other snug the chain up a little at a time till it goed away then try to maintain that setting over the life of each chhain. If its a used saw there could be other factors like a bent guide bar or a bad nose sprocket in the bar also a poorly resharpened chain can cause this