+1 for dunk's answer.... It has happened to all of us at one time or another.
Also maybe you are using a too aggressive blade on thinner wood. the fewer TPI (teeth per inch) the more aggressive the blade is. A high tooth count is better on thinner stuff.
Speed of the blade inters into the whole thing too. Try speeding up or slowing down the blade speed and feed a bit slower.
Sometimes even pushing the material to the side when cutting can cause the blade to catch and cause what I call "rattling" of the wood.
Hope some of those suggestions help you out.
Rog