Anoying noise!

[Ford Prefect]

Hi everyone,
I do not know, if I am in the right forum here, but I try:
I live in a pretty old building and record with a laptop. Most of the time there are interfering noises. So I guess it has something to do with electricity. But as soon as I touch the strings of my guitar the noise is nearly gone. This works with also works with any cable connected via USB (e.g. the cable of my MP3-Player). As soon as I touch the loose end of the cable, the noise decreases.
But the best thing is: I have a cheap metal watering can. I touch the can and the cable at the same time, the noise is totally gone.
As I am not very good at electric issues, I hope, I can find some answers here.
So where does this noise come from, and why does it stop, when I touch something out of metal?

So long and thanks for all the fish!

[jre3132]

Sounds like you probably need dedicated grounds for the power in your building. That would be quite a job though. An outlet with a dedicated ground is usally orange in color and referred to as clean power (thats kind of a quick run down, there is more to it).

Have you tried a ground lift? In case you aren't sure, they are the little gray or orange plugs that go on the end of a 3 prong plug converting it to 2. That could possibly cut a little of that noise out for you.

[Ford Prefect]

Thanks for the hint.
I forgot to mention, that I live in Austria. So the coulors of the cables are a little bit diffrent. I tried the ground lift already, but nothing changes. I took some "insulation tape" and interrupted the part of the power plug.

So any more advises?