I tried searching under generators but found nothing. Please point me in the right direction if this has been covered before. I just spent some time playing in a band in a field. We started playing before the generator arrived, so I used a 150W invertor with a caravan battery to power my Hartke HA3000 (200W into 8 ohms - 10 Amps peak drawn from the battery). I noticed that I had a high-pitched buzz, which disappeared when I touched the strings, so I tried connecting the signal-cable-ground directly to the invertor-case ground-lug. It made no difference. Turning down the tone control on my passive bass got rid of the noise. When the generator arrived (8kVA on a handcart), I thought that my problems would go, but I still had the buzz, and I could still get rid of it by touching the strings, or turning down the bass treble cut. As far as I can tell, the generator output was floating, and the generator chassis was earthed, since my portable RCD/GFCI refused to allow power up, because it could not sense an earth connection. Again, as far as I can tell, the Hartke audio circuit is totally separate from the mains and earth circuits - effectively, it floats too. What do I have to do to get rid of this hum?