Help: MM Stingray 5 strange hum

Hi
I have Music Man Stingray 5 ’98
(body was refinish to natural,
E02034).
There is strange hum/hiss in parallel mode (bridge position of 3-way switch). Also, when the selector is switched from single mode to parallel mode, click / pop will be heard.
What I did:
1. Tried connecting bass with different cables;
2. Inserted several brand new batteries;
3. Installed a new battery compartment;
4. Checked the soldering on the preamp and pickup, checked the wiring diagram;
5. My bass was shielding with copper foil.
But…hiss/hum stayed:(

I made a short video demonstrating the problem: MMSR5 hiss.mp4 – Google Drive