I bought a mechanic's stethoscope and have some interesting information:
1. The metallic knocking sound seems the loudest when I position the stethoscope on the vacuum pump housing.
2. It is loud when placed on the valve cover end closest to the radiator but still not as loud as the vacuum pump cover.
More background:
This started as a soft ticking and then got louder.
More importantly another symptom I've noticed is that the engine no longer comes to an abrupt stop when I turn it off with the key(what I would previously call normal). It kind of "dribbles" down to a stop.
The engine idles normal and visibly it's not shaking or rocking side to side..all looks normal except for the knocking noise.
As of this weekend the noise is not as loud as it was previously.
Oil quantity and pressure are normal when the engine is running.
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So the question is can a vacuum pump going south make this type of noise.
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It's a rythmic metallic knocking that increases and decreases with rpm's and does not skip. I think I'm narrowing this down to an injector or vacuum pump problem. Any ideas??? Especially about the possiblity of the vacuum pump being able to generate this type of noise. I think I may order the gasket and take it off and check it first.