Good idea. I´ve been trying to record it, but it comes and goes pretty fast and sometimes not at all, so it´s a bit hard.
Yesterday while using another amp, my phone got unplugged and I plugged it back in without lowering the amps volume or removing the headphones from my head: That actually made a similar sound to the noise in the S.E.X, but a bit lower in volume. So the noise is kind of similar to that crackling you get when you plug in or out the jack from a live amp. And earlier I´ve had some imbalance issues with speakers which I traced to the jack plug not "closing" proper to send signals to the speaker post.
I guess I should resolder the wires to the jack once again and maybe clean it out. Or maybe just change it out?