If the "off" taste from the rayon wick isn't a
dry hit (when everything else is okay, dry hits are often caused by not enough rayon wick in the coil, causing poor contact), the consensus here seems to be that an off taste is caused by
too much rayon wick inside the coil- as in too tight. When the rayon is at the right density inside the coil, the taste is good right from the start.
One other thing with your RTAs is to run the tails thinner than you would with cotton. Thick tails tends to pull caramelized
juice out of the coil between inhales, this causes the wicks to darken considerably- to the point that the juice will also darken. So if you see this happening you'll know you can go with thinner tails.