Monitor hum

[Navi]

so i have a pair of M-Audio StudioPhile SP-5B Near-field monitors. and i set them up and everything is dandy.

however, unless i have the volume on the monitor knobs jacked down close to zero, i get a very noticable low end hum from the monitors. i've been working around it by keeping the monitor volume down and jacking up my mixer, but it's still drastically softer than when I say...listen on phones. Is this just a flaw in the monitors or am i doing some thing wrong?

also, a side question: is it better to leave a preamp on or turn it off when not in use?

[zircon]

Crosstalk from other electronic devices, possibly?

[Patrick Burns]

Is your studio all on one power strip, or is it on multiple outlets? I'm not very experienced at all with this side of things, but my first guess is a ground loop.

[tgfoo]

Also, what types of chords are you using to connect them to your sound card? And how long are those cords?

And there probably won't be any ill effects from leaving your pre on all the time. I know my mic is almost almost always plugged in and active. I forget who ( I know it was somebody who makes a living recording other people at another forum I go to) but it was recommended to me if I wasn't going to put my mic away when I wasn't using it that it was better if I just left it on.