Sorry it's not a solution reply but I also get a short intermittent rattle on start up when car is almost cold. I've managed to isolate it to when the coolant needle is sitting maybe half a cm above cold. Doesn't do it when dead cold or at operating temp and doesn't make any noise at all when driving, just on start up. Half a second it's gone, sounds like a pulley to me so interesting to hear you've replaced pulleys with no success.
Some on here have said that VVTi gears or something to that effect can cause a rattling noise on that side of the engine. I'm not 100% certain of it is that how bad it is if these engines do have noisy VVTi gears. Sorry I couldn't help but if you do some searching on the VVTi thing you might see if it's a similar noise.