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Q: Rattling noise upon startup, slightly when idling, and constant during acceleration.

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I'm concerned it may be a timing chain tensioner because I've read that they do wear on a lot of these cars. I'm just not sure of the characteristics of a failed/damaged one. I do also have a check engine light for the bank 2 O2 sensor stating that it's running below threshold so I'm hoping that my catalytic converter has failed and components are rattling about inside. I do feel a slight loss of power as if it's exhaust related but I guess my question is, when the timing chain tensioner needs replacement, how often or when should I here rattling.

My car has 170000 miles.
My car has an automatic transmission.

A: The rattling may be coming from either one....

The rattling may be coming from either one. The only way to tell is to listen to see if the noise is coming from the timing chain or front of the motor. The catalyst noise would be mostly from around the exhaust area of the catalyst. If you have a bad tensioner or guides the noise will be there constantly but will be lighter or heavier as engine increases or decreases. A catalyst rattle may come and go and not really be as consistent.

I'd suggest you get some help from a qualified mechanic who can diagnose the source of the rattling noise and your Check Engine Light in person. Once the issue has been pinpointed the necessary repairs can be made.

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