GK MBs-lll ground loop when attaching pre and power chassis together

[mojotronix]

Hello,
Working on obtaining schematic, but in the meantime, I can't figure this out.
GK MBs-lll ground loop when touching pre and power chassis together.
Also, when referencing signal ground via input, effects loop, etc jacks to chassis ground, the bass guitar signal is muted.
Is the signal ground supposed to be floating on these?
Any help is appreciated.
Stan

[Jazz P Bass]

If this is the correct schematic, there certainly seems to be separate grounds for the preamp & the power amp

http://bmamps.com/Schematics/Gallien...ice_Manual.pdf

[mojotronix]

Thanks Jazz P, but the one I have is a newer design. Looks like GK will send me a schem when I get back to them with board #.
I'm sure GK didn't change the grounding scheme much though. Confused how the multiple ground planes are laid out. There is nothing referenced to chassis? Even through resistor/diode circuit?