oxygen sensor rattle

working on my sisters 2000 Grand Am with the 4 cylinder motor. I have a noticeable rattle on the oxygen sensor itself. looks like some kind of thin metal cap which the wire runs thru. tried turning this cap but it just spins. any clues? also seems to be a rattling in the pipe when hitting it with rubber mallet even when i'm able to hold this cap quiet.

Hey there, if the sensor itself is rattling in the manifold then i think you should either try to tighten it, or if you have not replaced it in a while just put a new one in. I know the silver cap your talking about the one that you can twist, this is normal its ok nothing to worry about. If you change the sensor and your using a oxygen sensor socket this allows you to move the wire to fit in the slot on the socket. to allow the socket to fit over the sensor.

its the sensor under the car in the exhaust and its tight, just the cap making noise. i'll just tell sis to turn up the radio louder.....works for all my GM stuff.