The same happened also to me :-(

It happens even, when the boot is done without any cable...

What helps: installing "gainroot", "sudo gainroot",killing the fmtxd with "killall fmtxd", and then restarting the fmtxd:
"fmtxd -d". Then it works!

(but needs to be repeated after each reboot, if the "fm transmitter" is to be used again...)