It certainly sounds like RF getting into where it doesn't belong. End-fed wires are notorious for bringing RF into the shack.
I would suggest trying to put a ferrite choke on the power leads and keeping them as short as possible.
Any external wires (PTT, Mic, key, power, headphones) might be acting like an antenna and allowing
RF in where it isn't wanted.
Is there any way that you can try a different coax fed antenna ? Maybe try the same configuration at a friends place where they
have different antenna setup ? That would at least allow you to rule out some internal issue in the radio. If you can't reproduce the
issue elsewhere with a real antenna on it then it is likely something specific to your use of the end-fed wire and resulting RFI.