2005 Tacoma a couple of problems

I have a 2nd gen 2005 tacoma double cab short bed. Has 105k miles. Is completely stock

1. I had P0430 Engine code which is Catalyst system efficiency below threshold (bank 2) Which is my driver side. I checked for leaks and checked the 02 sensor to make sure its working and all of that is good. So I think my CAT is bad to solve the problem I bought the URD 02 simulator and never had the check engine light since. But my truck is making some rattling noises when it is under load. It only makes noise when under load. It sounds like beads in the exhaust. I was thinking to get the CATS cut out. Im just annoyed of the rattling sound. Does anyone know what it could be? Can the timing chain make a loud rattling sound? All I want to do is get rid of the rattling sound.

2. I have this problem after starting my truck where there is a delayed engagement into D. When I shift from P (park) to D (drive) sometimes the truck will delay like 4,5 seconds and it will finally shift into Drive. But this only happens sometimes. Maybe like %40 of the time. I feel like this is a problem with the Shifter. The truck runs good and drives smooth and shifts smooth. I just dont know why there is a delay from going to P to D sometimes.