Have you ever been to a mechanic, told them your engine was making a knocking noise and had them send you home? Of course not. That’s not what mechanics do when you tell them your engine isn’t working right. They take it for the day, or two, test it and try to fix it. Sometimes they will do lots of tests, tighten bolts, change belts and there will still be a knocking noise. Sometimes, they will discover there was a loose marble in your trunk making all that noise. Sometimes, they will discover that your engine would have fallen out on the highway had you driven one more mile.