Oil Pump Pressure Relief Valve (aka Non-Return Valve)

Has anyone replaced one of these? Located in the oil pump, not the oil filter housing. Already replaced the oil filter housing relief valve. No improvement.

I'm chasing the daily, early morning M119 rattle. Goes away at the same pace the oil pressure gauge rises. Along with the rattle dying as the pressure rises, there is a squeal that rises in pitch and also ends at 3.0 bar. Every morning, every time.

No chain rattle. Rattle is from cam area. Squeal comes from the oil pan area.

So I'm getting ready to replace the oil pump pressure relief valve. Theory is the oil leaks past the relief valve overnight, and when re-pressurizing at startup somehow causes the squealing noise. Pressure's at spec while running. Just the engines runs dry overnight.

Valve piston, spring, and new plug (kit) costs $180 at the dealer and $120 at ecstuning.

Have searched every site, in every combination of terms, designations, ideas I can think of. Open to any suggestions. Thanks for your help.