CB Bleedover

[Ed in Tx]

Might be RF going back down the feedline getting into the house electrical system and maybe the speaker wires to that stereo which would explain why you are hearing your transmission while it's off. From your description and what I see looks like an old Antron A99 CB antenna. I have one I used on 10M that the fiberglass is shedding badly too. (I need to do something about that.) One thing that I did that helped keep RF off the feedline and getting back into the radio, was coiling up about 10 turns of coax just below the antenna feed point to make a common mode choke balun, but I also remember doing other things including the optional radial kit for that antenna before I mostly eliminated the problem. The coiled up cable forming a choke balun was the most effective in my situation.