On Fri, 6 Nov 2015 05:55:46 -0800 (PST), wrote:


(Maybe electrostatic shielding it looks to be on the caps right
after the rectifiers???)

My guess too.
Post-production development.
They have used an existing board fixing hole.
Possibly radiation into audio channel as one capacitor can will not be
at ground potential - although if the cap was doing its job...

Remove and listen for difference.