Yeah, something is wrong if you're getting any kind of shake from the engine. Now if you're just talking about that drumbeat effect some planes have at idle, you can't do much about that. But odd noises in flight are your one and only warning that things are about to start falling off the plane. The biggest mistake with these planes, as jetmech05 said, is people exceeding their maximum flight speed. You are flying a plane that is optimized to hang on its prop and put along at 10 mph doing so. It's not a sport plane to bore holes in the sky with. That's what they make Ugly Sticks for.