CF can shield an antenna from proper receiving, but having a rod or two should not cause an issue, by themselves. Having a full CF fuselage, or putting the antenna inside a rod would. That fuse is really tight, so it could be the carbon and all the other stuff (wires, servos, etc) in very close proximity that was reducing the ability of the antennae picking up signals .For my Kunai's, I have the two antenna from the receiver poke out through a hole on each side of the fuse just under the wing. I use a bit of heat shrink tubing to protect the wire from the edges of the hole (the edges can act like a saw and cut the wire). I almost never remove the wing, so the antenna are taped to the bottom of the wing.
BTW - a true brownout is low voltage to the receiver, usually either due to a bad battery or servos drawing more power than the battery can supply. VERY unlikely in the case of the Kunai. Perhaps a bad ESC (also very rare, especially without any other symptoms). Get the antenna as far away from everything else as you can, first.