318 stock,started making a small rattling sound recently now it sounds like a knock Does not get faster with engine rpm.Took the Alt., water pump belt off and no noise.Could the water pump a knocking noise.Used a long screwdriver as a stethascope and could here no knock anywhere.Am a little confused....

got another alt you could sub for a quick test to try & pin it down. agreed, I'd sure think a noise from either one of them would be RPM dependent, especially the pump. EDIT first unplug a field wire on the alt & see if it gets quiet

I took the alt.to a local parts store to test.While testing I heard no abnormal sound.It tested just fine...

Is the field wire the one you can just pull off.The connector was loosly fitted so I put a new end on and the noise is more eratic but is still there.

I've heard that before, and the water pump/fan shaft would be loose if wiggled. It was the bearing area eating itself up.
I once worked for a guy that had an old Ford truck, same racket that got pretty loud. He wouldn't fix it. When the water pump came apart, the noise stopped. But so did the cooling, not least of which was from the fan hitting the radiator.

if the sound doesnt change w engine rpm its not the engine or anything bolted to it

sometimes an alt electrical malfunction of a certain type (diode?) can make a squeal usually high pitched like a siren which certainly ain't the case here but it would take 3 seconds to pull it to elim that & swapping the alt would be easier than swapping a pump but the alt would do it at the parts house the same way (be making the noise) so but now the pump is looking guilty tho I would think the noise would increase with RPM

Or the fan clutch could be failing or even loose. With the belt off is there any unusual slop in the WP shaft or fan/clutch/spacer?

Just a little play.It does not seem to excessive,but it could be enough..