Static noise when enabling NC, and is this a reset hole?

My Bose QC20 has developed a static noise when NC is enabled and they are not connected to a device. If I touch the connector tip the static noise disappears, when I stop touching it it comes back. I used to use this headphones for NC only but now I can't as they static noise is very annoying. I think it must be a grounding issue but What can I do?
I have searched online and found the answers about cleaning the earpieces and making sure the screen in the earpieces is in place and not pushed inside. I did all that but that didn't help.
On the other hand, I realised there is a little undocumented aperture near the cable in the control module. It's like a reset hole, although different. see images. I tried to find what's that for but I haven't found any manuals or images that include that aperture. what's that for?? I was suspecting/hopping it's a reset button?

I've tried to press with a small screw driver. Try to cross what appears contacts, hoping it's a reset button, but nothing has changed. I've only tried this with the NC disabled in case I damage something.