Reply to S4 w. Logitech Speakers Buzzing?

Hi everyone, i noticed a little problem with my speakers/S4 today. When i turn my speakers up to maximum, so that i can control the volume with the S4 master, i get a lot of buzzing. When they are turned up to maximum and NOT connected, there's nothing. I got a pair of Logitech z2300, connected with a minijack 3.5, to a jack 3.5 to RCA adaptor, and then to the S4. I don't know if it's because they aren't simply meant to DJ with, or if they are just crap, but i hope some of you can help