Roland E-35 keyboard with temporary noise/hum

[marcinado]

I have a Roland E-35 keyboard that is working great, however after playing music, when sounds are stopping, then there's noise/hum for couple of seconds. Problem is very obvious on internal speakers. On "headphone output" is less significant and I can't hear it on "line output".
I couldn't find "E-35 service notes" in the Internet but E-35 have similar "CPU Board" and "GSE Board" like in E-70 model and "Power Supply & Amplifier Board" is like in E-15 model.
I think capacitor/capacitors are guilty but optically all capacitors on boards looks ok. Can you help me localize source of problem? Then I can unsolder some elements and check them in LCR tester.
I've attached example audio file which is amplified and you can hear that after 3 second hum is gone and only noise floor is present.

[Audiorepair]

I assume you have ruled out the external power adaptor as the culprit?

[marcinado]

Yes. Checked on two different power adapters.