I was tuning on my car and I heard the dreaded knock. I will not know for sure if its a spun bearing until I drop the pan but there is a good chance it i. Just for some info. there is main and rod bearings on your crankshaft they usually spin to lack of oil its the only reason cars can rev as high as they can, if one spins your engine basically needs to be replaced. If you run with a spun bearing your car will go till it has no power usually in a week or so, then much worse can happen like throwing a rod. If I have to pull the engine it might be semi salvagble, but if I was to reuse it again I would have to order a a rebuild kit, get my crankshaft cut and the thing about cutting our crankshaft is it has a nitrate coating and cutting it .o10 even can cause problems with the crank. This is no issue if you have a stock car, but mine is not. I was gonna use the money from the computers I was selling to buy me some cams. Something always bad happens, I just replaced the headgasket, head, and did a rebuild not to long ago.