SubjectSigma

I recently bought a 2002 Maxima with the 3.5 and a couple days after buying it my oil light started flickering at a stoplight. I babied the car home and upon arriving home I checked the oil level which looked fine. However for my sanity I did an oil change (5w30 Synthetic 5qts). That night I took a friend out to dinner with no issues. The next day I was on my way to work when I took it out of gear to slow down the oil light came on stayed on and the engine stalled. Starting the car again gave off a horrible knocking noise which my friend confirmed was a rod knock. Now I'm about to replace all the rod bearings but I can't help but think that there's an underlying issue. Is it oil Viscosity, the oil pump bad? I don't want to fix the knock and have the real problem stick around to ruin another rod bearing. Any advise is appreciated thank you.