Ok, this is a multiple part question:

After reading these threads, it seems there are several common rattles with specific RPM ranges when the rattle occurs.

I suspect an A-pipe rattle since I can't cause the rattle to repeat by shaking/hitting the exhaust. I have read that the A pipe usually rattles at around 3000 rpms. I do have a LOUD rattle that occurs at the 3000 rpm range as well as a lower rumbling rattle around 1800 rpms. Both of which quiet down significantly once the engine warms up. I also developed an exhaust leak somewhere around the cat a few months before the rattling appeared.

1) I realize that I might have two completely different rattles, but has anyone seen an A-pipe rattle below 2000 rpms as well as in the 3000 range?

2) If my leak turns out to be the cat gasket (i have seen several mentions of this in "rattling threads"), could that cause a loud rattle similar to an A pipe?