What Is That Noise?

[quality1as]

I have a 03 Tahoe 4.8 after having cat converters installed, the engine developed a knocking noise. Sounded like the second rod back. Removed oil pan, found aluminum shavings. Checked all rod and main bearings: like new. Removed timing cover and oil pump. dis-assembled oil pump, found it was badly scarred internally. It appears that is where the aluminum was coming from. Put it back together with a new oil pump. Same noise. Can't hear when cold, gets louder as it gets warmer, good oil pressure, you can hear it everywhere with a stethoscope, but still sounds louder in the front of the oil pan, can also hear it loud on the exhaust manifold heat shields, but I assumed it was an echo. Haven't killed injectors you to isolate. Wrist pin would get quieter when pistons expand with heat? No beaing material or steel from cam or lifters just aluminum. Any ideas?? Thanks