What Broke on both my Husqvarna 350 and Rancher 455?

Both Saws Run Great, Both HAve The Same Issue It Began As They Were Cutting, The Chain Would Get EXTREMELY tight For a Second, Then Back To Normal Tension, But Sound Like Rocks Under The Clutch Cover, Which Steadily Got Worse. Eventually The The Chain Wouldn't Even Spin But The Saw Is Still Running And The Horrible Sound Is Worse?? What Broke And Where Can I Buy Parts From Without Selling A Child To PayfFor it