What brand/model of monitor is it?

Wes

they are behringers

Im not sure the exact model though Im not at the studio. But they are behringer.It is strange cause it is not happening to the other moniter or sub-woofer?

Re: they are behringers

jamjunctioncom wrote: they are behringer.

nudge nudge wink wink

I had pretty much assumed they were behri#ger. check out this thread:

http://recording.org/modules.php?name=Forums&file=viewtopic&t=20230&highlight=behringer+radio

Reason 974,658 why I dislike Behri#er.

Wes

I have seen this same basic question asked on this forum in the past. Kurt Foster went through fairly elaborate steps to deduce what the cause was. Seemed that it always ended up being a problem inside a Behringer powered monitor. But if you tell someone, "Oh, it's just being a Behringer!", they take great offense at that.
I would tell you to open up the box and look at the connections inside it. There may simply be a ground wire that's broken off a connector. I can't tell you to open the box, though, if the unit is still under warranty. That would certainly void it.
What you might do is simply change you connecting scheme. For instance,don't connect the subwoofer. If there is a ground loop there, you won't have the hum if that is out of the picture. Play detective...