My 83 500SEL makes this rattling "metal BBs in a can" noise only when idling. I thought it was pinging/knocking but I don't think it is now. I'm using premium fuel, replaced the spark plug wires with new Bosch wires, new Bosch spark plugs, and ran a bottle of fuel system cleaner. I haven't checked the timing. The cap and rotor look ok and I don't quite know how to check if the ignition coil is ok.
The noise goes away when driving or under moderate loads. It idles at about 700-750rpm (normal).
Could I have a bad/clogged/broken cat? Would this be a symptom? The noise comes from there - right beneath the driver area. The cats aren't rubbing or touching anything to create the noise.
Also, the car seems to have some light white exhaust smoke for the first 5-10 mins of driving, even after it's been parked for only a couple of hours... would this be just condensation or could it be a leaking head gasket? It's steam white in color, not blue or black.
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