Noisy start up after switching to a different oil

Hey all,

Last oil change I decided to run a different oil than usual. I switched from valvoline high mileage 10-30 to castrol high mileage 10-30. Ever since the change I've noticed what sounds like prolonged piston slap in the morning. It takes about 5 minutes of driving (a fully warmed up engine) for it to go away. That seems like a long time for piston slap to be audible.I know piston slap is normal, but shouldn't it go away after a few seconds? The noise is most prominent at fast idle when the engine is warming up. Its still present below 1500 rpm just not as loud. When I'm driving, I can hear it until about 2500 rpm, then it goes away.

Oil level is where it should be and always has been.

Car: 99 LGT 5mt EJ25D

Mileage: 155,000

I live in California and the morning temps rarely go below 40* F.

Only thing I can think of is the t-belt tensioner knocking, but that would make noise all the time right?

Car runs and drive fine otherwise, the engine feels strong.

Any ideas?