Ive noticed this on my 4-cyl 1994 Camry for a while now, but couldnt be bothered thinking about until now
sometimes on startup the engine make a loud clank noise

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it almost sounds like one of the cylinders is hitting the top of the engine or something like that

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it doesnt happen all the time, ill say about once every 2 weeks it would do it.....
i doesnt matter if the engine is cold or warm when it makes the noise....
after turning the key and hearing that noise, the engine runs like normal....no difference in sound or performance.....
any ideas about what it could be?
thanks.