Need to eliminate static

[Rakuen Growlithe]

Recently I was trying to improve my laptop's sound. So I connected it up to an old (1970's) collection of audio equipment and ultimately to two big speakers.

I took a wire from the laptop's headphone port and plugged that into the microphone port on a Sony TC-366, which was connected to a Kenwood TK-40SW and then the speakers. That played everything fine and sounded great but if I do it when the laptop is plugged in to the charger I get a bunch of static interference (not loud enough to drown out anything but is really annoying).

I know very little about electronic devices so can anyone tell me how I can fix this?

[anoyomouse]

I get an electric hum on my soundcard when i plug in my sound system and turn it up to REAAAAALY loud, but it's not safe for human listening

i stick with my machine using it's built in speakers, (which has a sub that vibrates the frame of the laptop), or i just play things via the digital on my 360

[Rakuen Growlithe]

Mmm... I could do that. But compare the sound quality of a laptop speaker that's not even the size of my hand and two speakers, in wooden boxes, that are each probably bigger than my laptop.

[Rakuen Growlithe]

For anyone who's curious I learned what's wrong. As I imagined it obviously has something to do with being plugged in. Apparently normal current has a lot of interference running through it while batteries give clean power. Also the way I was connecting things was running a signal through an amp twice and so boosting all the junk in it. Apparently to fix it I need to buy a filter for the plug before it gets to the laptop. I've never heard of that though but yeah.