loud rattling noise upon start up but then goes away

Yes. I also inspected the main and rod bearing and did not see any apparent damage. I did however just notice quite a bit of sludge in the bottom of the oil pan which could possibley clogged up the sifter screen but not sure if that could be the problem?

Cant tell by looking if pump is needed!! Replace pump and pickup tube. Clean sludge from pan. Pump is in the front of the engine driven by the cranksfaft, right? It is possible the relief valve is weak, but it comes with the NEW pump.

How can you tell if is weak? I attempted to disassemble the old pump, but could not get the phillip head screws to come loose, but I did get the spring and cap loose and removed and did not see any apparent damage either. I removed the pick up tube and observed the rotors from the pickup tube inlet hole and did not see any apparent damage to the rotors either, but I may be wrong since I can not get it completely disassembled. Could there be something else internally other than the rotors that I am not seeing? Thanks for your help, by the way