PBMagnet, The aroma oil cup is a Copper plumbing fitting. Actually an end cap.
There are plenty of sizes from tiny to large available. That is a 1/2" fitting and I believe (from pictures) that Woodeez uses a 3/4" fitting. Obviously I had a choice of size. And so do you, any hardware or Home Depot type plumbing department will have tons of them cheap. <$1
I am not going to say who is right, niether is 'right', but I will give you my thinking on size. The larger 3/4" fitting is about 7/8" diameter and nearly blocks the entire top hole. The Purple-Days fitting (1/2") is 5/8" diameter.
I considered what blocking the natural convection flow of heat might do... Since the unit is designed to sit open and maintain it's temperature, blocking this natural convection may increase temperatures. Not say it does, just giving my thoughts, during design. Since the unit runs on the high side of vaporization temps (IMO) to start, any increase wasn't something I was after. So I went with the smaller cup, which would allow the air to flow around it rather than be blocked by it. The other point is, it's meant to hold a few drop of oil, not be filled, so cup capacity isn't an issue.
I try to think things through, I may not always be right, but there is always (I hope) some thought behind my actions and the consequences they may produce.
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Anybody who builds a Pandora, please, if you run into trouble, like PBMagnet, with his snapped wire, or just a question, give us a shout (via e-mail). Even though the kit has no warranty (since you are the builder), we want you to have a completed, working product that is built right. If you break or loose a part (it happens), or just can't figure it out (it happens), be honest and tell us (in a short note), we try to help everyone.
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Pretty tough to speculate on a "small rattle", on a unit I didn't build, and not being there to hear it, but it may be the resistor hitting the heat exchanger wall. It may be the wires hitting the through holes. It could be a droplet of solder from construction or a piece of wire that you cut off. Hard to say.