I have a 92 Teg GS.

Happening for about 4 months now. Random Time. Engine could be hot or cold.
Normally I notice it when I start up in the morning and then went I start to
pull away from the driveway, the noise begins....sounds like it is coming
from the driver side engine area. The problem is I can't quite catch it
cause everytime I put in in park to get out and open up the hood to check,
the noise goes away. I don't know how to explain what the noise sounds like.
It's almost like tapping but much higher pitch than the valve taps and quite
rapid.

Already got mechanic to check alternator belt and tightened it.
Water pump is fine I think cause the engine is not overheating. But this
could still be the water pump. I just don't know how easy it is to exactly
pin point it to the water pump.

Thought it may be the air conditioning compressor (cause my air conditioning
had no R-134a left) but now I just got it recharged. However, the sound
still occurs.

Any ideas out there?

I did noticed on a really hot day, after I highway driving and parking the
car, the ABS fluid reservoir was overflowing.  It wasn't leaking but
overflowing out of the reservoir cap.  Don't know what could have caused
this? Now I noticed that the ABS reservoir is below the MIN line. So I will
have to refill with ABS Dot 3 brake fluid. But do you think that the ABS
system could be causing the weird noise?

Much appreciated.