So, I might have found a solution for this high frequency noise. It requires a screwdriver, aluminum foil, electric tape and two hands. In my case, it came from the electronic of my bass, I guess. For this tutorial I assume you already have a shielded cavity, if not, DYI or bring your insutrment to a tech to do so.
Keep reading for the whole process, for the short solution scroll down.
I did the thing of swapping the ground with the sleeve, no result, with or without the Line6 adapter. This is the video of the issue I send to line6 support: Noise video
Sadly, the answer was: we're sorry, it is not compatible... Thanks for the effort line6.
So I asked the manufactor of my bass (the amazing Maruszczyk) and we talked about the noise, how it came out,so we made a test:
- Bass-->cable-->tuner pedal-->transmitter: no noise.
- Getting the transmitter close to the female jack: noise (see pic.)
So the transmitter is getting interference from the electronic (no noise in passive mode).
He then suggested to wrap the electronic with aluminum, which I did, checking for continuity. Sadly, this went bad, as you can see here Noise with shielded electronics
I started playing a little with aluminum foil and I eventually came up with the solution:
SOLUTION HERE
You can do the whole process with the instrument plugged in so you can real time hear if it works or something bad happens.
Step1
Take the female jack out of the cavity and put some tape on the outside of the tip pin (the one carrying the signal) so that the whole connector is insulated from accidental grounding (see step 2). If you don't do this right, you might experience no sound at all once everything is plugged.
Step 2
Take a strip of aluminum foil and fold it 2-3 times so it gets a bit thicker. Wrap it aound the female connector. I made it large enough to touch the outer metal part of the connector and once inside the cavity to touch the inner shielding of the cavity. You can use some tape to ensure continuity. Again, in the whole process aluminum foil must not touch the hot wire/tip or you'll get no sound. Use insulating tape properly.
Step 3
The most effective. Take more aluminum foil (same 2-3 layers) and cover the inner hole as much as you can, leaving just a tiny space for the cables to get through. Use tape to ensure continuity between the inner cavity and the newly applied aluminum patches. Everything has to be connected for this to work. Try not to stuff aluminum too much inside the cavity, although doing this a little bit might bring better results. What you need to avoid, again, is for aluminum to touch the tip/hot signal.
This is the final result. WIN
(I know, my amp is hissy, but I set treble and tweeter all the way up to maximise noise for diagnostic purpose).
Hope this helps other people, although you'll have to change the design a bit accordingly to how your guitar is shaped.
Cheers :)
