Speakers loud pop when powering cabinet & momentary voltage on GND plane

[keropi]

Hiya!

I finally started putting stuff inside my wooden cabinet - a POLO 28" monitor - a groovymame pc with JPAC and 2.1 Creative speakers. When I press the power button on the cab the tube/chassis and speakers get power and turn on. There is a 2nd push button that starts/stops the pc in the cab.
When I power on and the chassis does it's deguass stuff there is an annoying loud pop (parasite-like) from the speakers.
I also noticed that the ground plane of the chassis has voltage that quickly diminishes completely after 1-2 secs . The same happens on power-down - no speaker pop/parasite since the power gets cut-off from the switch but there is diminishing voltage on the ground plane (I only have an electrician's test screwdriver here atm so I just see the test light dying slowly)

The tube/pc work fine after that but I didn't leave it on for much time just in case there was a leak or something. My theory is that the speaker parasite is because the chassis dumps current on the ground plane during degauss and after power-down the bleed capacitor also dumps current at the ground plane again.

Is this the case or I should start looking for a short-circuit?   
I have stopped working on the cab atm because I don't want to kill anything   

TIA for any help/tips!

edit:
solved it's normal after all - a good friend confirmed after looking at the polo schematics and mentioning that test screwdrivers are not the best tool for checking this