69 Vette Engine Noise

My 350/350 engine was rebuilt about 25,000 miles ago. The car runs well without any loss of power. However, there is a slight tapping noise coming from the engine. I've been told by several mechanics that the
noise is probably not serious. I've also been told by one or two people that with 25,000 miles on the rebuilt engine, it should not be making any noise. And I've been told that the kind of noise coming from my engine is common.
At any rate, I'm not prepared to have the engine rebuilt again at this point. Has anyone else had this engine problem? What are some things I, or a mechanic, can do to try to eliminate the noise?
Thanks, Charles
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Charles Halliman wrote:

IMHO, a noticeable noise is worth investigating, especially if it becomes more audible over time; it may mean a component is loose, and catching it early could save big expenses later. Without listening to the engine, none of us could say whether the noise you're hearing is "normal" or not. Nor did you say WHEN the noise is most noticeable, ie, when idling with the hood up, when accelerating, on hills, when cold, etc, etc..
A little lifter clicking noise may be acceptable with solid lifters, but you really shouldn't be getting particularly noticeable noise from only one or two of your hydraulic lifters. If it IS a lifter, that's easily remedied. A definite tapping or knocking is not a good sign, but the "tapping" noise could be coming from something external like a loose flexplate bolt or a loose spark plug wire, or a waterpump belt, fuel pump, exhaust manifold or head gasket leak, dented valve cover, etc, and not from a vital component like a rod or lifter or valve or piston or timing chain. You need to determine the general area of the noise, and estimate it's frequency with respect to the engine rotation speed (every rotation, every other rotation, etc), then investigate further (remove the valve covers, uncouple a spark plug, or whatever) to further pinpoint it and assess it's threat to the engine.
Get a mechanic to investigate by using a stethoscope to determine the probable source and go from there. A hundred or two spent on diagnosis now could save $$$ later, or it could just give you peace of mind.
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