driving back from dealership with Vantage v8v on cruise when I would go downhill car would small backfire or more like an exhaust quiet pop. Like unfired has in chamber firing. Thinking of bottle of Marvel Mystery Oil in gas. Had 2 Tire & Service centers when working and seemed to keep valve rattle to a minimum before done auto. Thanks Frank

 

Normal operation, no magic in a bottle fixes it. Put more fuel in it and keep driving it.