I use my polished SS Dreamer in 18650 mode and have zero battery rattle or arcing.
The delrin sprung battery adjuster should take up any slack, but if you are having to wind out your 510 on the RDA to get rid of rattle (I hope the 510 is adjustable on that RDA, otherwise you will have a loose post) I would suggest that the silver firing pin in the switch is at its limit of travel when making contact, and not making a solid connection when you press the button.
A solution is to unwind the firing pin half a turn or so, to raise it, which will lengthen your button travel but make a more solid connection with the battery when the button is pressed.
You will need to clean the arc marks off those batteries, because they are little raised points, which will cause more arcing.
A pencil eraser, fibre glass pen, scotchbrite or even the green bit on a washing up sponge should do the trick, but be careful not to damage the battery wrap or insulator.