Metallic coolant?? symptom of what?

Let me start off saying that I believe that I have a flow problem as the slant gets hot while on the hwy, but I noticed while checking the coolant level in the rad, that it was metallic, very fine pieces of metal in the cooling system. So, what should I be looking for as the cause.

list of pertinent info:
/6 with 180* thermostat changed when I put in the new water pump around Christmas time. ( heater inlet on the water pump was plugged)
22" stock radiator with 2 speed electric cooling fan.
10* initial timing ( vac can is still hooked up but it's dialed about 5 turns out. )
carter BBD