HELP My STX38 quit on me. I was mowing along just fine and all of a sudden SNAP CRACKLE POP and it quit. It did start again but sounded so bad I shut it off in a hurry. Towed it to my garage, let it cool a bit, and tried it again. It POPPED LOUD through the muffler but did "sort-a" start. I let it cool a bit, and tried it again. There is a very prominent "Knock" when it turns over. I have been considering getting a new 370, 380, or maybe a 5XX series mower, maybe it will be sooner than I thought. Does this one sound completely dead, or is this enough information to tell. I am not familiar with tearing down and rebuilding a motor, but I thought maybe I could get some guidance on checking things out. Model #CV13S Spec # 21509. Thanks for any help. Greg