Hey Ryszard,
I've just had an unpleasant thought...

To set the background, I have a time share ownership in a "luxury houseboat", and it is pretty good I must say.

...but there is a slight problem. Being a boat, there's no real ground one can tie the on board power to. Power on board is supplied by 12V batteries connected to an inverter. The batteries are charged by a 240V, 2000W Honda generator via a normal battery charger (actually, 2 fairly smart ones - there's 2 battery banks)

Anyhow, that's all to set the scene for my HP notebook and really BAD noise when connected to the inverters.

My particular model of notebook has the mains earth extended through the charger and into a 3rd wire in the connector to the notebook. I assume it's some protective arrangement.

I MUST disconnect from the charger to stop the noise, and I note it's REALLY bad.

I believe it's caused by the floating earth (pun not intended... Oh alright, it WAS intended smile ). If the boat's ground were properly earth staked I believe the problem would either not exist or be considerably reduced. By really bad I mean it almost totally drowns out the music!!!

This has made me wonder if the ground in your house might be resistive enough to be floating a little above 0V. It's not an uncommon thing you know. You might try locating your earth stake and pouring a bucket of water over it, paying particular attention to where it enters the ground - try to get that quite wet.

--=-- My credo: If it's worth doing, it's worth overdoing - just ask my missus, she'll tell ya laugh --=--
You're only paranoid if you're wrong!