Metal pickup ring grounding issue

[gingataff]

Hi Guys

I put a screamin demon and lil 59 in a guitar, wired with a 5way mega switch from
A schematic from the dimarzio site. I made sure to change the wiring colours from dm to sd, but I get terrible buzzing when I touch the metal mounting ring for the bridge pickup. The easy solution would be change to a plastic ring but I'm thinking this is probably a more serious grounding issue.

Any advice on how to proceed?

Thanks!