On my '05 3Valve, it is as others mentioned, the tensioners not having enough oil pressure on startup causing the timing chain to rattle. This problem was addressed with tensioner upgrades that had improved O ring sealers. It has been recommended by the U Tube " Makuloco" channel, who I highly respect/recommend, to use 30 weight oil to help with the many problems the first series 3Valve had. But for the chain rattling problem on startup that some of these motors have, I have gone back to the factory recommended 20 weight and this has eliminated that problem, at least on my engine, which was making that noise from 46K miles when I got it. With 110 on it now & the 20 weight, no more noise, ever.