2006 Nissan Xterra Losing Oil Pressure and Clattering

[CDV]

I have a 2006 Xterra. It has smoked when I first crank it up since it had 50,000 miles on it. It has 110,000 miles on it now. It was running bad (no power) and they said it was the catalytic converters, so I changed them and all of the coils. Now it will run for a few minutes and the oil pressure will drop down to 0 and it will start clattering. It sounds like the bearings not getting oil on them and the crank. I cut it off wait a few minutes it will run for a bit and then do the same thing. Does this sound like the oil pump or the timing chain cover issue? Thanks,