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2003 Ford Explorer Catalytic Converter

Long story short. A loud cow bell clank when I first start and drive every day then it stops. When I park the SUV, the pinging begins (for about an hour -very loud). Same thing, everytime I start it, it will clank about 10 times and stop. Took to Ford - 3 days later, they cannot figure it out - they definitely hear it - just can’t find it. Replaced the heat shield. Still does it even more so. Was told they probably tested the catalytic converter and disturbed it even more. Should I get 2nd opinion, replace it? or be happy to trade it in - has 90,000 and is as clean as a whistle otherwise. Not sure what to do -don’t want to pay all the money if that is not what it is and they are only guessing.

No check engine warning lights and Ford can’t locate.
Explorer has an upstream and downstream O2 sensor.
If upstream is failing, the downstream sensor will report via check engine warning light. Failure of upstream sensors and continued operation will cause failure of the cat.
Testing the cat means banging on it and listening for loose components.
Not heard.
Drive on and pay attention to check engine warning light.
Clean as a whistle means changing upstream O2 sensors at 100k.

Thank you. I took it to a regular mechanic last night and he laughed at the thought that it was the cat too. They are looking at it on Friday. I backed it up this morning and it ran for about 5 minutes while I was grabbing something and the regular pinging began. It is the noise that I hear when I back it up and then forward - the cow bell clang - it happens like I said about 10 times, then I dont hear it at all - repeats at night when I leave from work. Hopefully someone will be able to figure the noise out - I dont mind paying to have it fixed but Fords “we think” for $1400 is not my idea of fun. The other mechanic told me the cost was nuts too. I appreciate your input and will make note of it.