My cobalt ss makes a rattling intermittently at start up and is only heard outside the car. Coming from the Timing chain side of the engine. In addition it makes a knocking noise while driving at about 2200 rpm to 3000 rpm, usually after sustained driving and usually under load. Seems to clear out after I get it to knock a few times and raise rpms. My guess is timing chain and tensioner, but any information would be helpful thank-you in advance.<\/p>\n","protected":false},"excerpt":{"rendered":"