Oldsmobile/Buick Repair: Coolant loss and accelration, coolant loss, fan blade

Question
Hello Van-

I'm driving a '77 Buick Century Special V6 231cid.  Over the last month or so I've been experiencing frequent coolant loss and a rattling noise when I accelerate that sounds like shaking a can of spray paint.  The rattling also occurs in park and neutral but not in reverse until I accelerate.  Also, 3 days ago I discovered a small puddle of coolant behind my driver's front wheel.  I asked a mechanic buddy of mine what might be the problem and he told me to check the hoses and radiator for cracks and ruptures.  I didn't find anything and I'm still loosing coolant.  I've also checked the water pump weep hole for dripping and the telltale residue of burned on coolant but didn't see anything.  I've also ruled out the thermostat by performing an immersion test.  My question is this: could the rattle and the coolant loss (especially the recent "puddle") indicate a water pump failure even though there are no "obvious" signs of seepage?

I'm at my wits end here - any help you can provide would be fantastic.  

Answer
Hello Matt,
If the rattling is water pump related, you should be able to tell by wiggling the fan blade front to rear.

The coolant could also be leaking from a block freeze plug.

The flywheel flex plate, on an automatic transmission, can crack and rattle.

Van