Does tubed gear make your speakers hum/buzz?

I've just started using my first piece of tubed gear. It's a Dared SL-2000A pre-amp. I've had it running in the system for about a week now. I really like the improvements this has made to my system.
My only is problem is that I just noticed that my speakers make this humming/buzzing noise when the pre-amp is on but no music is on. It's only noticable when you put you ear right next to the speaker but I still don't want it there. I'm not using any power condition on my system and I'm in a highrise apt building in NYC. Could this be the cause or does it have something to do with the tubes? I'm currently using it with the tubes that it came with.

By the way, I already tried the 3 to 2 prong,,,,,,didn't work.

help.

meech