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as I am sure you can appreciate, it is difficult to diagnose a noise one cannot hear.
common causes of noise like this would be the lifters (more of a tapping though), one of the belt driver components, or the oil pump. usual diagnosis steps are to run the car without the belts briefly to see if the noise persists and to trace it with a mechanic's stethoscope.
if the noise does not change with engine speed, it could possibly be an emissions control pump, so in that case the pump would be disconnected and the car started to see if the noise still exists or not.
the only next step is a proper fault scan and test plan.
Sorry if you were hoping for a different answer, please don't shoot the messenger - I can only give the honest answer, which I have. Please remember that a low rating PUNISHES me for my honest and prompt response, and I receive nothing for my time and answer until a positive rating is clicked.
Please let me know if you have further questions. Please do not forget to click a positive rating as this is the only way I receive credit for my answer, thank you. Best wishes with your vehicle