Purchase yourself a mechanics stethoscope and try to pinpoint the location of the noise.
You can find them online (Amazon) and at most automotive parts stores.
Hydraulic dampers & rocker arms should not make any noticeable noise as you described.
Could the noise be in the timing belt area?
Have you tried removing the serpentine belt and running the engine without it to see if the noise goes away? Rules out a lot of items!
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Supporting Vendor and Moderator of LOST05 Jeep Liberty CRD Limited
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