I have a rattle. I happened to notice it when I had the hood up and gave the throttle a couple of bursts. At idle I can't hear it, but I can hear it reasonably clearly when the engine is sitting at 2000 plus revs. However its most noticeable, briefly, when the engine quickly decelerates after being revved hard. Its quite a metallic sound. It could be a noisy bearing, or maybe its just an ordinary metallic rattle from the exhaust. (Yes I removed the dreaded Y piece baffle a couple of years ago.)

Anyway, I'm not particularly asking for advice on what this rattle might be. I guess I'll find it eventually. I'm more interested in hearing your special tips on how to find the location of a rattle. I often find it very hard to zero in on the source of a rattle. The old plastic tube or screwdriver to the ear trick is pretty awkward!

I just bought a mechanics stethoscope on Ebay. For $6.50 including postage I figure I theres not much to lose.

Maybe try doing a video of the engine and get the rattle to show up then we might be able to track down some ideas for ya

You might not believe this but sometimes the rubber drive belts can sound like big end bearing knocks. True that! I can never use stethoscopes because there is that much mechanical noise going on it's difficult for me to hear the noise I'm after.
Cracks in exhausts/heat shields are known to squeal or rattle too as well as small stones inside exhaust shrouds. Torgue convertor drive plates can crack, rattle or screech.

Just some ideas.